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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 181854
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
254 PM EDT Thu Apr 18 2019

.SYNOPSIS...

A warm front will lift northeast across Pennsylvania later 
today. A slow moving cold front will push into the region Friday
bringing a widespread soaking rain. It will then remain 
unsettled at least into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...

An area of showers and thunderstorms is racing NE through the
NRN Mountains as of 18Z. It is along the leading edge of the low
level Theta-E gradient/warm front. The HRRR and high res NAM do
not see it so model depictions of dry weather lasting well into
the evening are not as convincing as they otherwise would be.
Regardless, with this feature moving quickly into NY, we kept
only small chances for additional showers in the forecast
tonight.

Otherwise, the strong spring sunshine has melted the low clouds
almost completely away leaving scattered to broken mid and high
clouds moving quickly NE under the strong flow aloft. Visible
loops show a swirl over SW PA, a remnant MCV???

The southerly breeze will increase overnight. Most of the area
should be mild and dry in the warm sector, with the best chances
for showers being over the far W and NW after midnight.

Min temps overnight will be quite mild - in the 50s and lower 
60s.

&&

.SHORT TERM /FRIDAY/...

Increasing deep-layer SSW flow ahead of a sharp upper trough 
and an intensifying sfc low moving through the Ohio Valley will
help to transport significantly higher PWAT air into the region
priming the airmass for increasing coverage of moderate to 
heavy rain and embedded thunderstorms.

Models are showing marginal instability but potent deep layer
shear ahead of the low and wavy front that will be moving into
western PA by nightfall. SPC has inched the SLGHT Risk into my
far southern counties, and the feeling is that they will likely
keep creeping the outlook northward in time. 

Strong winds just off the deck and low LCL heights will produce
the threat for damaging wind gusts along with an isolated 
tornado given the impressive shear and helicity.

Heavy rain will also be a threat in the increasingly soupy
airmass with the GEFS lighting up much of my eastern CWA with a
high probability of at least 2 inches of rain in 24 hours. HPC
has highlighted all of eastern PA with a slight risk of
Excessive Rain, prompting the issuance of a Flash Flood Watch
for tomorrow afternoon and evening for my eastern zones.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
A deep low lifting northward across the Great Lakes will tend to
slow down and cutoff at some point late this week or early next
week. This system will pull a cold front across the area late
Friday into Saturday. 

The heaviest rain Friday afternoon into early Sat is still
expected to exceed 2 inches across portions of our eastern CWA,
with 1-1.5 inches across the west. 

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 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.

Overall, just minor adjustments made to the forecast.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...

Mainly VFR conditions will continue overnight, with lower clouds
beginning to overspread the flying area late at night.

A storm system and wavy front will move into the region late 
Friday and Friday night producing widespread showers and 
thunderstorms. Some of the rain could be heavy and some of the
storms could be severe. E

Expect widespread sub VFR conditions to accompany the 
increasing chance for rain and thunderstorms during the day into
Saturday.



.Outlook...

Sat...Widespread restrictions in the morning with PM 
improvement and continued scattered showers.

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

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

&&

.HYDROLOGY...
Rainfall from showers and thunderstorms on Fri/Fri night 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 Friday afternoon through Saturday 
morning for PAZ028-036-037-041-042-046-049>053-056>059-063>066.

&&

$$
SYNOPSIS...La Corte
NEAR TERM...La Corte
SHORT TERM...La Corte
LONG TERM...Lambert/Martin
AVIATION...La Corte
HYDROLOGY...