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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 180934
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
534 AM EDT Thu Apr 18 2019

.SYNOPSIS...
A nearly stationary front stretching across the Central 
Appalachians and Middle Ohio River Valley will lift northeast 
across Pennsylvania as a warm front later today. 

A slow moving cold front will push into the region Friday, and 
will interact with an extensive plume of deep, tropical moisture
to bring numerous showers and thunderstorms Friday into early 
Saturday. 

Expected rainfall amounts of 1 to 1.5 inches are likely across 
the Western Mountains of Pennsylvania, while heavier, 24 hour
totals of 2 to 2.5 inches, with locally higher amounts should 
fall across the eastern half of the state.

&&

.NEAR TERM /THROUGH TONIGHT/...
Compact, 70 kt upper jetlet lifting NE across the Commonwealth
early today was helping to form a few small clusters of fast
moving rain showers. Rainfall occurring over brief 5-10 minute
periods (mainly this morning) will be limited to several 
hundredths of and inch or less. 

Temps across much of the Northern and Western Mtns will warm by
6-8 Deg F while delta Ts from between yesterday and today's
highs in the Central Mtns and Susq Valley will be 15-17F higher
this afternoon.

Look for sunshine, mixed with varying amounts of altocu and
cirrus clouds across the western mtns of PA, while thicker/lower
Stratus and Strato CU (present this morning morning within the
CAD regime across Central and Eastern PA0 gradually dissipates
from the south and west this afternoon as mean llvl winds veer
around from the SE to the South.

The southerly breeze will increase tonight, with increasing 
strength of gusts (over and just to the north of the higher 
ridges) as standing waves tap and transport the belt of 
stronger 40-45kt SSW wind (present at just 1-2 kft AGL) to the
sfc in gusts of 25 to 30 mph.

Chance for showers will be minimal in the warm sector tonight as
the upper flow slowly backs to the SW with the ridge of high
pressure aloft building along the Mid Atlantic Coast. However, 
the approaching trough over the Grt Lks, could support a few 
showers over the northwest portion of the forecast area.

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
sub-995 mb sfc low heading NE up the Ohio River Valley will help
to transport significantly higher PWAT air into the region
priming the airmass for increasing coverage of moderate to 
heavy rainbands and embedded low-topped, fast moving TSRA that
could tap the relatively high values of 0-3 km helicity
exceeding 300 m2/s2 to display supercell structure at times. Low
LCL heights, combined with the presence of transient llvl 
boundaries from numerous rainbands, will produce the threat for
an isolated tornado or two given 0-1km EHIs ramping up to over
1.5 M2/S2 over portions of central and eastern PA (within the
strong 50-55 kt southerly, 850 mb wind max). 

&&

.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 /09Z THURSDAY THROUGH MONDAY/...
VFR will continue to dominate the weather pattern overnight for
the western and central TAF sites. The Eastern TAF sites of 
IPT, MDT and LNS will see MVFR cigs overnight through Thursday 
morning. Cigs will lift as the morning continues though some low
cloudiness may linger into the aftn in the east.

Low pressure moving through on later Friday into Friday night 
will produce widespread showers and thunderstorms. It could 
remain a bit showery into the weekend, as upper-level low 
pressure slowly passes overhead.

 Out ahead of the approaching system will be a low level jet
which should cause some Low level wind shear. Have mentioned it
between 09Z to 21Z at BFD with it affecting the TAF sites mainly
through the east TAF sites after 00Z Friday. 

.Outlook...

Fri...Mainly VFR AM, with deteriorating conds by aftn with 
SHRA/TSRA developing.
Fri night...Widespread restrictions in SHRA/TSRA.
Sat...Widespread restrictions in the morning with improvement 
thru the day despite scattered SHRA lingering.
Sun...Scattered SHRA persist.
Mon...Mainly VFR. Late-day showers possible.

&&

.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...
None.

&&

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