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FXUS61 KCTP 210847

Area Forecast Discussion
National Weather Service State College PA
447 AM EDT Mon Oct 21 2019

This week will feature more dry days than wet days with rain
expected on Tuesday. Seasonably mild temperatures on Monday 
will trend modestly cooler through midweek and remain near 
average through the weekend. 


Low clouds and fog this morning should give way to a partly to 
mostly sunny afternoon. Sfc obs and RWIS data indicate areas of 
dense fog/lowest visby AOB 1/4SM being observed over the higher 
terrain from the Laurel Highlands into the Endless Mountains. An
SPS may be issued through the morning commute. Lower elevations
to the east of the Allegheny Plateau are primarily dealing with
low clouds with some patchy fog in spots. 

The main forecast issue today will be timing low cloud
dissipation. HREF data indicates the south central ridge and
valley region will take the longest to erode and not fully 
break out until after 16-18Z. The earlier an area breaks out of
the clouds, the more upside they will have in terms of maxT.
Overall, expect the mildest readings in the mid to upper 60s on
the northwest and southeast fringes of the CWA with the coolest
temps (around 60F) over the interior high elevations along the
Allegheny Front.

Fcst soundings suggest the potential for a few sharp dewpoint
drops given mixing of very dry air just above the inversion 
layer. This is mostly likely to occur over the northwest mtns 
where skies will be mostly sunny. 

Clouds will increase into tonight with an increasing south 
southeast flow ensuring very mild minimum temps running +10 to 
+15 degrees above average for late October. 00Z HREF shows the
leading edge of frontal rains reaching the far western zones by
12Z Tuesday. 


Confidence remains very high in a band of rain moving west to
east across CPA on Tuesday. The strong south-southeast flow will
transport 1-1.5 inch PWAT air (+2-3 standard deviations above
the mean) into the region and support widespread soaking rain.
Instability (MUCAPE) appears to be negligible (so no mention of
thunder) but the deep moisture available should allow for 
locally heavy downpours. NBM/WPC blended QPF amounts are still 
in the 0.50 to 1.00 inch range with the highest totals most 
likely over the favored southeast flow/upslope areas across
east-central PA. A secondary low developing over the Delmarva
and tracking to LI may enhance rain should bring the last round
of rain to far eastern/northeastern zones btwn 00-06Z Wed before
pcpn shuts off west to east across the CWA by the predawn hours
Wednesday. Flash flooding is not expected given the recent 
dryness (3hr FFGs 2-4+ inches) and limited rain rates in the 
absence of deeper convection. However, can't rule out some very 
minor nuisance type street flooding or ponding in urban areas 
due to leaves clogging storm drains. 

It will turn mostly sunny, breezy and cooler on Wednesday behind
the departing frontal system. High pressure will provide dry wx
through Wednesday night with some potential frost/freeze risk
for southeast zones still active in the extended growing 


There is reasonable consensus among the guidance in showing some
light rain/showers skirting across the eastern Great Lakes and
possibly clipping the northern tier of CPA on Thursday. However,
pattern evolution uncertainty grows quickly heading into the
weekend with very low confidence in the forecast at this time. 

The global model guidance continues to offer 2 possible 
solutions by this weekend: 1) a less amplified GFS with weaker,
faster system with little to no rain; or 2) a stronger and
slower system with a much higher probability of rain (later
Sunday into Sunday night) advertised by the ECMWF/UKMET/CMC. 

Until there is a convergence/trend toward a common solution, the
wide range of outcomes results in a very low confidence forecast
which leans on gridded data from the National Blend of Models. 


At 04z, showers now just about gone over the SE counties with 
low pressure sliding east away from the region. Area of low 
clouds evident on satellite imagery over much of the southern 
mountains extend northward on the east wide of the Allegheny 
Front. These will persist much of the overnight and will take 
some time to mix out on Monday. In addition, eastern areas that
received rain earlier and find themselves in clearing skies 
will see valley fog develop (it just moved into IPT at 0330z). 
So, IFR/MVFR cigs/fog will impact portions of the eastern 
2/3rds of the CWA overnight, before a gradual mixing out to VFR 
conditions by late morning Monday. SE winds do pick up across 
the west on Mon to speeds around 10 mph with gusts to 15-20 mph.

A return to wet conditions on Tuesday. Then improving 
conditions after Tuesday, as weak high pressure builds into the 


Tue...Rain/low cigs possible.

Wed and Thu...No sig wx expected.

Fri...Some showers possible, especially west late.





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