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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 191214
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
814 AM EDT Fri Apr 19 2019

.SYNOPSIS...
A slow moving cold front will push into western PA late today 
bringing numerous showers and thunderstorms, which will produce 
heavy, to locally excessive rain across the eastern half of 
Pennsylvania. 

The cold front will take until Sunday to move east of 
the Keystone state. It will then remain unsettled on Easter 
Sunday into much of next week. Much of the time from Sunday into
mid week will be dry, but no long term dry spells are seen at 
this point.

&&

.NEAR TERM /THROUGH TONIGHT/...
Warm sector and dry conditions blanket all of the region early
this morning and expect these conditions to last through the
prime morning rush hours in most places. 

Temps just prior to dawn are quite balmy and in a rather tight
range from the upper 50s to mid 60s.

We have just scattered to bkn mid and high clouds streaming
quickly NNE across the CWA with light south to southwest winds
in most valleys locations, with gusts of 20 to 30 mph on the
ridgetops. 

Look for increasing the thickening clouds as we head through 
the second half of the morning with isolated to scattered late
morning showers, becoming widespread and ocnly heavy during the
early afternoon hours (south) and mid afternoon (northeast).  

Increasingly Neg tilt upper trough and strengthening deep layer
shear will lead to moderately strong upper diffluence/large
scale uvvel. Selective areas of higher ML cape and favorable 
forcing by terrain/llvl boundaries will cause scattered TSRA for
form and be capable of heavy rainfall rates in excess of 2
inches per hour. 

Maintained previous configuration and timing of the Flash Flood
Watch for this afternoon and tonight. The strong, southerly 
wind Field aloft will be easily tapped by thunderstorms with 
wet microbursts and localized strong to damaging gusts possible 
within the broad Marginal Risk area that covers the southern 
two-thirds of the forecast area. 

WPC has expanded the Day 1 Slight Risk area of Excessive Rain 
westward a bit to cover all but our Laurel Highland and NW Mtn 
zones. However, the most persistent and highly anomalous soupy 
PWAT air over plus 3 Sigma (and plus 3-5 sigma 850 mb moisture
flux) will reside across the Susq Valley and points east, so 
refrain from a slight wwd expansion of the FFA for now. 

The very mild start to the day will translate to afternoon 
maxes that will be in the upper 60s (nrn and wrn mtns) to the 
low-mid 70s (Central Valleys and Susq Region). These temps will 
average 10-12F above normal.

&&

.SHORT TERM /SATURDAY/...
Falling heights and gradually cooling temps aloft ahead of a
slowly filling upper trough and weakening/elongating sfc low
will mean plenty of multi-layered clouds and sctd-numerous rain
shower coverage for much of Saturday into Sat night. 

QPF will average anywhere from several hundredths of an inch in
some locations, up to around 2 tenths of an inch in others. a
few clusters of locally heavier showers and even a low top tsra
can't be ruled out Sat afternoon and evening, which could bring
a few locations between 0.25 and 0.50 of an inch.

Max temps Sat will cool by just 2-5 deg F, and will still be 
several deg or more above normal.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
While it will start off mild, the Easter weekend looks to be 
cold and wet. Best chance of dry and sunnier conditions will be 
later on Easter Sunday.

Another cold front expected on Monday, followed by high 
pressure trying to build southward. Still some chance of showers
at times, given the front being nearby.

See hydro section below for more detail on the potential for 
heavy rain.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...


An approaching storm system will spread showers and 
thunderstorms into central PA this afternoon into tonight. 
Localized downpours are expected, and a few of the storms could 
produce gusty winds. Expect widespread flight restrictions 
Friday afternoon into Friday night.

Unsettled, showery weather will persist into Saturday and 
possibly Sunday as well.

The other aviation weather concern is that out ahead of this
advancing front there will be a low level jet which will bring
low level wind shear. The worst of it will be overnight until
around 15Z at BFD, IPT, MDT and LNS. 

.Outlook...

Sat...Widespread restrictions in the morning with some 
improvement despite continued chc of showers.

Sun...Scattered showers and areas of sub-VFR.

Mon-Tue...Mainly VFR with scattered showers.

&&

.HYDROLOGY...
Only minor changes made to the QPF at this point.

Flash flood watch remains in effect for this afternoon into 
Saturday morning for the eastern half of the CWA.

Rainfall from showers and thunderstorms today and tonight  
could be enough to produce flooding, though mainly on tribs of 
the Susq Mainstem and North Branch, where MMEFS shows 4-5 points
of concern for exceedance of minor FS. 

Storm total QPF via model consensus and EFSs has decreased
slightly since 24 hours ago, but still in the 1-1.5 range across
much of Central and Western PA, with locally 2-3 inches expected 
across the east between Noon Friday and noon Saturday. 

Latest runs having that convective look to the precip with big 
stripes of heavy/intense rain and gaps in between. No solution 
in particular should be followed verbatim when it comes to QPF. 
Model solutions generally keep the heaviest rain over the east, 
with relatively lighter amounts elsewhere. 

The larger waterways (Susq, Juniata) should be fine until at 
least Saturday or Sunday if they ever get high.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from 2 PM EDT this afternoon through 
Saturday morning for PAZ028-036-037-041-042-046-049>053-
056>059-063>066.

&&

$$
SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...Lambert/Martin
AVIATION...Ceru/Evanego
HYDROLOGY...