Synopsis...
Large duel-wave system, including the remnants of Nicole, moving up the east coast on Thursday will send copious amounts of moisture and precipitation across almost the entirety of the Mid-Atlantic region. Low pressure system and associated frontal boundary will move out during the day on Friday and a trough sets up shop for the weekend.
Short term (18z Thursday - 12z Friday)...
A slight difference from the previous forecast is that most of the models, including the SREF ensemble data, show a slight trend westward on the tracks of the low pressure systems moving up the coast. The GFS, NAM, ECMWF, and the ensembles all show the remnants of Nicole going just east of the spine of the Appalachains, bringing essentially a perfect setup for heavy rainfall across central-eastern Pennsylvania. State College has seen around .40" so far with reports out of Lancaster of over 2" within a 3-hour period between 6 and 12z. Trickiest part of the forecast is pinpointing the tight gradient in precipitation over western-central portions of the state. Am currently thinking that heavier amounts can extend as far west as a Johnstown - Clearfield and northward line (with amounts of up to 3-4" possible). PWATs across the state are well over an inch given the strong conveyor belt of tropical moisture riding up the stalled frontal boundary over the eastern US. As for eastern sections of the state, the SREF total precipitation amounts have a whopping 6-8"+ mean rainfall range over a line from Harrisburg - Scranton from about 12z Thursday - 12z Friday, quite unkown territory for the ensemble means. I expect this to verify given current strong convergence zone over northern virginia and eastern Maryland on current observation sites. It still looks like far northwestern sections of the state will see mostly very light precipitation from this event, but the 6z WRF has heavy precipitation just to the east of Erie and Meadville, whereas the GFS and SREF have heaviest precipitation farther east. Flash flooding will likely be a widespread problem across the Susquehanna Valley over the next day or so. Temps will be around 60 in the far northwestern sections of the state and in the mid-upper 70's in the southeast near Philadelphia for highs today - that may be the simplest portion of the forecast.
Long Term (after 12z Friday)...
As for the longer term, after the front and Nicole move out, a trough establishes itself over the northeast later Friday and into the weekend cooling temps down quite significantly into the upper 50's and lower 60's for highs on Saturday and Sunday across much of the state. WRF and GFS hint at some type of light precipitation on Sunday between 0z and 18z across much of the state but this should not be significant. We'll need a break after the rainfall the state gets in the next 24 hours...and the entire Mid-Atlantic for that matter.
Forecaster: Kyle Imhoff
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