Forecast Discussion

Updated 3:34 pm EST,  Friday, 10 Mar 2017 by Patrick Saunders

NEAR TERM (Today/tonight)

Generally upper level northwesterly flow will persist for the near term and likely into the short term which I will discuss in the next section. Relatively clear skies have allowed the sun to warm temperatures a few degrees higher than what most models were predicting. GFS/NAM has low temperatures around 23 while the RAP has it lower (around 20) which isn’t unusual for the RAP. What’s unusual is MOS guidance predicting significantly lower temperatures (around 15) than their operational counterparts. Both the GFS and NAM has some late-night cloud cover around 09Z and modest winds between 5-10mph. This combination will likely inhibit maximum overnight radiation cooling. I don’t think MOS guidance will verify unless we have clear skies and isolated areas of calm winds, although there isn’t any indication that this will occur.

SHORT TERM (Saturday-Monday)

As mentioned in the near-term section, upper level northwesterly flow persists throughout the weekend. A shortwave trough is advected from our west to our south which will likely produce snowfall through the great plans region through the Tennessee valley into the mid-Atlantic region. Significant cloud cover will build in over the region on Saturday which likely moderate day time temperatures. After the shortwave passes Saturday night, surface high pressure builds in for Sunday, creating relatively clear skies and light winds. Things start to get interesting for Monday though. A short wave will move southeasterly through southern Indiana Sunday night, Monday morning which will be associated with a surface low moving through southern Indiana on Monday. There is a large of array of solutions being produced by the models. The GFS has a widespread area of 3-5” across Indiana. However, this seems like a pretty significant outlier compared to the ensembles and the ECMWF ensembles. Using Lafayette as a proxy for the state, the operational GFS has ~4” for Lafayette while the GFS ensemble mean for Lafayette is about 2” while the operational ECMWF has less than 1” and the ensemble members have around 1”. It’s a classic GFS vs. ECMWF situation. The low merges with a developing low off the coast and comes very close to bombogenesis criteria. This will likely produce significant impacts in the Mid-Atlantic and Northeast areas.

LONG TERM (Tuesday-Thursday)

Following the passage of the low pressure and development of a high pressure to our west, fairly strong northerly flow will create some strong CAA, meaning we could see temperatures down into the teens and isolated single digits Wednesday early morning. This high pressure will propagate south of us and should hinder and precipitation development over Indiana for the remainder of the long term period.


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