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Wxchallenge discussion

this page will host daily "blog" posts related to the Wxchallenge forecast

25 Oct KSDF forecast

posted Oct 25, 2012, 2:54 PM by Michael Baldwin   [ updated Oct 25, 2012, 2:54 PM ]

fun forecast, I always love these "midnight max/midnight min" days.  strong cold front currently in central IL is expected to pass through KSDF tomorrow morning, close to 12Z.  precip should begin shortly after the front passes and continue for ~8h or so.  expecting their max temp to occur at 06Z tonight, so the question is: what's the temperature going to be at 06Z tonight?  MOS and meteogram guidance going for low/mid 60s, it was 61 there last night at 6Z, stronger winds ahead of the front tonight will likely slow radiative cooling, so the 63-65 range indicated by MOS guidance sounds good to me.  sometimes you'll see temps go up a few degrees after the cold front passes in a night-time FROPA due to strong mixing behind the front and a cooling inversion ahead of the front. however, since this fropa not expected until close to sunrise, the "midnight max" appears to be most likely.  with the strong cold advection during the day/evening, min temp should occur tomorrow night at 06Z, again MOS and meteogram guidance is pointing at mid 40s for a min, somewhere between 43-47 seems reasonable.  models are pretty consistent with QPF, very close to 0.40" for all of the guidance. Purdue WRF is showing a bit more, something like 0.60".  Winds will be a bit tricky, plenty of mixing and gusts behind the front, meteograms and forecast soundings show ~20-22kts just above the surface during the afternoon, that momentum should be able to make it to the surface.  lots of spread expected with all of the numbers today, not sure if everyone will pick up on the midnight max/min issue and will go with MOS values which are 12h min and 12h max values, those will be terrible forecasts.  So expecting consensus to be something like 60/48/20kts/0.4", should be an opportunity to separate yourself from the pack with a good forecast today!

24 Oct KSDF forecast

posted Oct 24, 2012, 1:34 PM by Michael Baldwin   [ updated Oct 24, 2012, 1:34 PM ]

not a lot to say about tomorrow, thicknesses and 850 temps are slightly lower tomorrow afternoon than today, pressure gradient tightens up a bit as a trof develops ahead of the strong cold front that should move through that region on Friday.  I'm getting the impression that it is difficult for the min temp to drop below 60 there, guidance again is pointing to mid/upper 50s, but 60 seems like a good number to me.  I'm think the max temp will be ~2 degrees lower tomorrow than today, and max winds will be a few kts higher with the pressure gradient getting stronger tomorrow.  Consensus will be around 80/60/15kt/0.00" and I don't think there will be very much spread.  

23 Oct KSDF forecast

posted Oct 23, 2012, 2:16 PM by Michael Baldwin   [ updated Oct 23, 2012, 2:18 PM ]

similar story to yesterday, moist air is still to the north and west of KSDF, remnants of MCS are heading their way, but diminishing as the afternoon continues.  last night's 00Z Purdue WRF looks to have a very good handle on this (12Z is still sitting in the queue) as does the 12Z NAM.  main difference between today's forecast and yesterday's is there is no vort max heading their way tomorrow.  models show ridging overnight in the wake of the short-wave trough that is almost overhead.  with dewpoints currently in the upper 40s (!), they could radiate a few degrees cooler than they did this morning, tricky aspect of the min temp forecast is what will happen with what's left of the convection that has been heading their way all day.  I'm expecting some cloud cover early tonight, then clearing, so decent radiative cooling potential.  Dewpoints could rise as the convective remains pass by. Mid/upper 50s look good to me (similar to GFS MOS: 56 and current NWS: 57). Main question for max temp is: will they break their record (82)?  I think a tie is a good bet for tomorrow, thickness edges up slightly tomorrow, plus full sun should add a degree or two to today's maximum.  Guidance is showing low 80s, current NWS forecast is 82, that sounds like a good number to me.  Winds are predicted to be slightly weaker tomorrow, NAM meteogram not showing much potential for momentum mixing, so I'm thinking of something in the 10-12kt range.  Without any forcing for lift, precip does not appear to be an issue.  My prediction for consensus is 82/58/10/0.00", the min temp is the trickiest aspect of this forecast in my opinion, so I expect there to be more spread for that number than the others, but another day of relatively "sharp" forecast distributions.  Tomorrow will be a similar story (tempted to copy/paste this discussion, will anyone notice? go ahead and enter identical numbers for the day 2 forecast...maybe a couple more kts of wind), so we'll have to wait for Thursday's forecast (of Friday's cold FROPA) for the next opportunity for precip, tricky temp forecasts, and some strong winds

22 Oct KSDF forecast

posted Oct 22, 2012, 2:19 PM by Michael Baldwin   [ updated Oct 22, 2012, 2:24 PM ]

moving on to the next city: Louisville, KY, closest city to Purdue that we'll see this year

current obs/SPC mesoanalysis showing a large anticyclone parked to the SE of KSDF and a plume of high dewpoints that has advanced as far north as KLAF this afternoon in the wake of the MCS that moved across IL/IN today.  Satellite showing some cirrus across southern IN near what's left of that MCS. Dewpoints in northern KY are actually lower than here in central IN, lower/mid/50s with temps in the upper 70s/low 80s in the region.  Last night's low was around 60, not expecting much change tomorrow compared to today looking at temps/thicknesses, so current guidance calling for upper 50s for a min seems reasonable.  Similar argument can be made for max temp, persistence should be a decent forecast (near 80), consistent with guidance values.  Precip is an issue tomorrow, NAM and 12Z Purdue WRF showing next short-wave trof/vort max heading into Missouri tonight, WRF develops another MCS tonight and takes the remnants of that predicted system over northern KY during the day tomorrow.  There is currently some convection over OK just ahead of this vort max.  CAPE values are high across Missouri, and shear will likely increase as the mid-level speed max moves into that region tonight.  Not finding much support for the WRF's forecast in the latest HRRR, but it seems reasonable to me to expect another round of MCS development overnight tonight, whether the remains of that system will hold together long enough to bring some precip to KSDF is yet another tough question.  If that does occur, it could hold down their max temp a couple of degrees, the WRF doesn't bring those remnants through until late in the afternoon.  A few more knots of max wind would likely be the case if this scenario does in fact come true.  Given the low POPs in guidance values (and NWS) I doubt too many people will have precip in their forecast, so my prediction of consensus is 80/59/12kt/0.00".  I'm not sure if the payoff is worth the risk in terms of buying into the WRF's solution for some light precip, so I'm leaning towards zero and maybe knocking a degree off of the max figuring there might be some clouds later in the afternoon given the PVA with this short-wave trough.

18 Oct KBIL forecast

posted Oct 18, 2012, 2:37 PM by Michael Baldwin   [ updated Oct 18, 2012, 2:37 PM ]

current obs/SPC mesoanalysis showing sunny skies and light winds this afternoon in the wake of the strong, vertically-stacked system that has moved east towards WI, ridge building aloft and weak warm advection currently found at 850mb.  Next shortwave trough is expected to move north of MT, with pressure falls and an increase in the pressure gradient, expecting winds to pick up again tomorrow afternoon (although certainly not as much as earlier this week).  A decent warm up is expected with winds out of the southwest and thicknesses/850 temp increases consistent with a 12-15 deg F increase in max temp, the NAM forecast soundings are showing some moisture aloft in the afternoon, so those high clouds will likely prevent them from hitting 70 tomorrow, so upper 60s sound reasonable to me.  The min temp tonight will likely be affected again by momentum and mixing with the winds predicted to remain around 10 kts overnight, the general warmup compared to yesterday should result in a min temp that is several degrees warmer than this morning, the guidance is saying upper 30s and that also sounds reasonable to me.  Forecast soundings showing well-mixed PBL about 1km deep, hitting a weak inversion at 800mb with nearly dry-adiabatic lapse rates to 650mb above that inversion.  There's about 20kt of momentum that could/should mix down to the surface tomorrow afternoon, won't be surprised to see gusts to 25kt so the max sustained wind will likely be somewhere in between.  Precip is not an issue.  I'm thinking consensus will be very close to the current NWS forecast of 69/40/20kt/0.00", not expecting a lot of spread, so it will be tough to gain ground again tomorrow as we wrap up our forecasts for Billings, MT!  Louisville is next, will we have any "home court advantage"???

17 Oct KBIL forecast

posted Oct 17, 2012, 2:42 PM by Michael Baldwin   [ updated Oct 17, 2012, 2:42 PM ]

missed the past couple of days, too much going on to post a discussion, looks like everyone's doing fine without these discussions
problems of the day: min temp and max wind
current obs/satellite showing strong winds continuing today with pressure gradient relaxing to the west of KBIL, some broken clouds across the region, temps in the 50s with dewpoints in the 10s.  min temp tonight is tricky, guidance generally showing lower 30s, but NAM meteogram is getting them down into the mid 20s.  15-20kt winds are predicted to continue past midnight, then decrease towards morning, the enhanced mixing should prevent great radiative cooling, but the NAM is saying they could drop down into the 20s towards sunrise as the pressure gradient slackens and winds die down below 10kt.  not a lot of change is predicted for max temps tomorrow when compared to today, thicknesses are predicted to increase slightly, but with weaker downslope flow I don't expect a lot of change at the surface, so something close to persistence should be fine.  precip is not an issue.  max wind speed could occur around midnight while the stronger pressure gradient remains in place, or during the afternoon tomorrow when the boundary layer mixing could bring some of the ~20kt momentum from the top of the PBL down near the surface. Either way, the max winds will be considerably lighter tomorrow compared with today.  My prediction of consensus is 54/31/20kt/0.00" (basically the NWS forecast and very close to NAM MOS) with a sharper distribution than we've been seeing lately, not as much opportunity to gain ground/separate from the pack with today's forecast.

11 Oct KBIL forecast

posted Oct 11, 2012, 2:36 PM by Michael Baldwin   [ updated Oct 11, 2012, 2:41 PM ]

today's challenge: min temp

cold air, low stratus, and easterly winds locked in place all day at KBIL, but things are expected to change considerably tomorrow as the surface anticyclone is predicted to rapidly move off to the east overnight.  winds at the surface are predicted by NAM meteogram to switch from east to west right around 06Z tonight, southwest flow near the surface should pick up during the day as a weak cyclone approaches the area from the west.  after staying stuck in the 30s all day, they should easily warm up into the 70s tomorrow with full sun and downslope flow.  min temp tonight will be very tricky, their temps will likely stay stuck in the mid-upper 30s while the low cloud deck remains in place, but could warm up a bit overnight once the winds shift and some of the downslope flow taps into the warmer air above the surface.  I think it will be an interesting meteogram to look at tomorrow morning.  NAM meteogram has them cooling off to near 30 by sunrise, seems a bit wacky given the surface winds that it is predicting, and MOS guidance is well above that (more like mid 30s) not to mention the USL forecast of 42 for their min.  My confidence is very low on the min temp, my thinking is that they'll stay around 35 all evening until midnight, the winds will shift and skies will clear and temps will hold steady if not increase a bit as the winds pick up.  I've got more confidence in the max temps, full sun and downslope flow should allow them to develop a deep boundary layer tomorrow afternoon, allowing their temps to rapidly warm up into the mid 70s.  Guidance values are in the 74-77 range, I'm leaning towards the upper end of that range, thinking we'll see a similar situation to Tuesday when they warmed up beyond most forecasted values.  Winds will be somewhat of a challenge, the pressure gradient is not very strong once the current anticyclone moves away, but they will be well-mixed over a deep (2.5-3km) PBL, so some of the better momentum should mix down to the surface, similar to Wednesday when they saw gusts up to ~30kts and max sustained of 24kts.  I will probably go a couple kts below that.  Precip is not an issue.

So, for what it's worth (I'm better at predicting consensus than I am predicting the actual weather) I think consensus will be something like 75/35/20kt/0.00" with a large spread in the min temp, some potential for gaining ground if you do happen to be on the correct side of consensus

quick update: just read the AFD from Billings and they mention the possibility of fog...not sure if there ground condition is moist there, could see some ground fog developing which often makes the temps lower...just another tricky factor to consider for their min temp!

10 Oct KBIL forecast

posted Oct 10, 2012, 1:10 PM by Michael Baldwin   [ updated Oct 10, 2012, 1:10 PM ]

strong cold front currently along the Canadian border poised to dive south overnight, bringing a complete shift to the weather at KBIL.  Currently, to the north of this front, temps are in the 40s with overcast skies and some light precip, south of the front skies are clear with temps in the 60s.  Model forecast quickly brings this front through KBIL this evening with winds shifting around to be out of the NE overnight and for most of the day tomorrow.  NAM QPF shows some light precip over most of the state during the day, with a good easterly component there upslope flow, so expecting low clouds for (almost) the entire day tomorrow,  With fast flow aloft, the anticyclone is predicted to quickly move off to the east, pressure gradient should switch the winds to more of a southerly component by sunset, so there could be a brief hour or so of sun to throw a potential curve-ball at us for their max temps.  Another tricky issue: guidance values for temps are all over the place again today, GFS MOS has their min temp tonight getting down to 31, NAM MOS shows 37 (NWS agrees) which is more consistent with meteograms which are showing upper 30s.  Clouds should arrive well before sunrise, so it is possible that they will not even drop below 40 overnight.  Max temp guidance valuees are all in the low 50s, although NWS currently has a max of 48, which seems reasonable if you are going with overcast skies for the entire day.  Hard for me to believe the POPs in MOS guidance are so low, below 10% in both GFS and NAM, even with NAM meteogram showing 0.01" during the day tomorrow.  NWS POPs of 30% look much better, although doesn't look like there will be much more than 0.01" of precip, so it won't have much of an impact on your score either way if you decide to go zero or a hundredth (or two).  I won't be surprised if they end up seeing several hours of light drizzle adding up to a trace, which is scored as 0.00".  Winds are predicted to remain relatively light, considering the decent pressure gradient that is a bit of a surprise to me, NAM BUFKIT soundings showing ~15kts at 500m above the surface during the day tomorrow, it will be tough to mix that momentum down to the surface given the cool/stable air.  I expect the consensus values to be around 51/36/12/0.01" with a decent amount of spread in the temperature values given the wide range of MOS numbers that we're currently seeing.  I got "burnt" Monday going too cool, so the temptation for me will be to go a bit warmer on the max temp, I'm going to try to resist that temptation.

9 Oct KBIL forecast

posted Oct 9, 2012, 12:08 PM by Michael Baldwin   [ updated Oct 9, 2012, 12:08 PM ]

low clouds are beginning to break up early this afternoon at KBIL, personally hoping they will hang in there for a few more hours to keep today's max temp out of the mid 50s.  however, we don't do "wishcasting" here, right? 

forecast challenges today: max wind and temps

strong NW flow aloft expected to remain in place for next day or two with KBIL located on the west side of the deep trough that is sitting over the Midwest U.S.  surface anticyclone currently right over/just south of KBIL should move quickly to the southeast tonight, flow between the anticyclone and the cyclone dropping south will set up a decent pressure gradient over MT during the day tomorrow.  forecast soundings/time-height cross section show SW flow near the surface and westerly flow in the mid levels, should be plenty of downslope flow which will warm them up considerably when compared with today.  weak subsidence/plenty of dry air expected, so precip is not an issue.  NAM forecast soundings/meteogram show a well-mixed PBL tomorrow afternoon with surface temps getting to 21C (close to 70F).  this is several degrees higher than current MOS guidance (NAM&GFS: 63) and NWS forecast (66), although I expect the NWS will be going upper 60s when the next forecast is updated.  NAM forecast soundings show max wind at the top of the PBL around 25kts tomorrow afternoon, the PBL height is ~2500m, so I don't expect to see sustained winds that high tomorrow, I'm leaning a few knots below that number (but won't be surprised if the max gust ends up a couple of kts above that number) (note: we are forecasting max sustained wind, we aren't forecasting max gust).  NAM also showing low level winds shifting around to the SW before midnight and maintaining 10kts all through the night, this should prevent them from optimal radiative cooling, but this could be a tricky forecast since skies are expected to clear and dry air should be in place overnight.  Guidance/MOS is all over the place for their min temp (GFS: 36, NAM:41, USL: 43) I'm leaning towards the higher end of this range given the wind prediction. 

I'm thinking consensus will be near 67/39/20kts/0.00" with a bit more spread than what we've been seeing lately on the temps and wind

8 Oct KBIL forecast

posted Oct 8, 2012, 11:59 AM by Michael Baldwin   [ updated Oct 8, 2012, 11:59 AM ]

ok, we are done with Pensacola, FL and are moving out west to Billings, MT

Billings sits in the Yellowstone river valley, with major mountain ranges in nearly every direction:
the Bighorn mountain range to the south/east, Pryor mountains directly south, 
Beartooth mountains to their southwest, Crazy mountains directly west, Big Snowy mountains to their northwest,
and Bull mountains directly north

their temps have varied considerably during the past week or so (for example: max on Oct 2 was 82, snowed on Oct 3, 
max on Oct 4 was 44), and they've already had their first snow of the season
that should give you a good idea of how quickly things can change at Billings

looking at their climo: they have a decent diurnal cycle during the fall, with normal max/min of 63/40 and record max/min of 87/17

The NWS site has a nice link to surface/mesonet obs for the region

Current obs and SPC mesoanalysis show clouds and relatively strong cold advection in place in the wake of a cold front that is associated with a cyclone currently located in northern MN.  Some precip can be seen in the latest radar image just to the north of KBIL, they have also received 0.01" of precip during the day today.  Models are predicting precip to last through the evening hours tonight and perhaps beyond 06Z, which gets into the beginning of our forecast period.  Cold advection is expected to continue ahead of a surface anti-cyclone with is predicted to move into the region during the day on Tuesday.  NAM forecast soundings continue to show relatively high RH values during the day tomorrow, indicating cloud cover for a good portion of the day, with RH values dropping during the afternoon.  NAM BUFKIT soundings/meteogram brings their max temp into the lower 50s tomorrow, but other guidance (GFS MOS, USL, NWS) keeps them in the upper 40s, this seems reasonable to me with some broken clouds expected during a good portion of the day.  With a weak pressure gradient as the surface high settles in, guidance is indicating weak winds for the day, strongest wind may occur at midnight tonight while the precip is coming to an end.  Overnight min temps in the upper 30s are indicated by NAM meteogram with MOS guidance going for lower 30s.  They look to be clearing out tomorrow night and NAM meteogram has them just as cold if not colder tomorrow at 06Z than overnight tonight.  Mid 30s seems reasonable to me with the clouds/precip expected overnight.  Low POPS/not much precip is expected after 06Z, I don't think you'll be penalized much either way if you go with 0.01" or 0.02" vs. 0.00" 

I think we'll see a bit more spread in the numbers compared with KPNS, I'm thinking the consensus will be around 49/35/10kt/0.01", I would advise sticking fairly close to those numbers since most of the errors will be in the temperature values (in other words: only go a degree/kt or two higher/lower to be consistent with your forecast thinking) there should be opportunities to separate from the pack later in the week with a strong front predicted to drop in from the north on Thursday.

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