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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 200725
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
325 AM EDT Sat Apr 20 2019

.SYNOPSIS...
A slow moving cold front will move through the region later
this evening and overnight. Unsettled weather will hang around 
through the weekend as the associated upper air disturbance 
crawls eastward. Much of the time from later Sunday into mid 
week will be dry, but no long term dry spells are seen at this 
point.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Last counties removed from SVR Watch #92. As SVR/TOR threat 
winds down, still some hydro concerns as line of locally 
training convection in rich PW environment lifts up the Lower
and Middle Susq River Valleys through the early morning hours. 
PW in excess of 1.5" surging north on the nose of a southerly 
35-60kt LLJ ahead of negative tilted upper trough and strong 
upper diffluence/large scale uvvel. Selective areas of higher 
CAPE support scattered thunderstorms capable of heavy rainfall 
rates in excess of 2 inches per hour. The window of heaviest 
rain will be closing by around midnight with the HRRR taking the
deepest convection east of the CWA. Scattered showers will 
continue into Saturday however.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY NIGHT/...
Dry slot should bring a decrease in shower activity east of the
Alleghenies to start the weekend. Despite some clouds, high
temps should manage to peak around 70 degrees from the central
mountains into the Susquehanna Valley. Cooler temps and most
likely area of showers should be across western PA. Saturday
looks like the better day for the upcoming holiday weekend. 

Falling heights and gradually cooling temps aloft associated
with slow moving upper level low will spread shower risk to the
east across most of central PA on Easter Sunday into Sunday 
night. Temperatures will trend cooler but max climo departures 
are only about 5 degrees from mid April averages.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Expect improving conditions/dry wx early next week as high 
pressure moves into the area behind departing upper level low. 
Look for a nice rebound in temperatures with highs in the 65 to 
75 degree range on Tuesday. 80F not out of the question in the 
Lower Susquehanna Valley Tuesday afternoon. 

There is decent model agreement in the next frontal system
moving into or through the area around midweek. Beyond
Wednesday, guidance shows a large divergence in the evolution of
the boundary and overall precipitation pattern. Trends seem to
lean toward wet vs. dry into the second half of next week but
confidence is low. Temperatures are likely to cool off from
Tuesday's highs before trending warmer into next weekend.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Observation trends and guidance favor continuation of IFR
conditions at KBFD/KJST with MVFR to low VFR elsewhere. Vis/cigs
may drop at or below airfield mins at KBFD into the predawn
hours before recovering later this morning. Not much on radar at
06-07Z but hires guidance seems to be focusing on shower bands
setting up across the southwest and southeastern edges of the
airspace by 12Z. Used VCSH as initial hedge and will update with
more definitive FM or tempo groups as showers develop. Overall
trend is toward prevailing VFR by this afternoon into the
evening. Some restrictions are likely later tonight into Sunday
across the western airspace.  

.Outlook...

Sun...Scattered showers. A.M. MVFR/IFR cigs wrn 1/3 trending 
VFR.

Mon...A.M. MVFR cigs psbl N/W. Chance of showers ern 1/3. 

Tue...VFR. P.M. Showers/t-storms psbl NW 1/2. 

Wed...SubVFR psbl with showers. 

&&

.HYDROLOGY...
Trimmed western portion of the flash flood watch as heavy rain
threat has ended. Watching band of rain lifting northward toward
Chesapeake Bay that may clip the far eastern counties. Latest
HRRR/RAP indicate potential for another stripe of heavy rain
(1-2 inches) through mid morning. 

Through 20/06Z, observed rainfall axis (1 to locally 2 inches) 
extended from the Juniata basin and western lower mainstem 
Susq. tribs northeast into the WB tribs and upper mainstem Susq.
This has produced small stream rises to near or just above 
bankfull levels at a few non-fcst points. Sherman Creek crested
just below minor flood stage. 

The Swatara creek points have missed the heavy rainfall and 
therefore odds/confidence of minor flooding has trended lower.

Several-foot rises are fcst on larger rivers with fcst crests
near to above caution/action levels at Harrisburg and 
Williamsport later Saturday into Sunday night.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 11 AM EDT this morning for PAZ037-041-
042-046-049>053-057>059-066.

&&

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