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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

                            
000
FXUS61 KCTP 200516
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
116 AM EDT Sat Jul 20 2019

.SYNOPSIS...
----Dangerous heat and humidity expected through Sunday---

We will be dealing with hazy, hot and very humid conditions 
until early next week when some relief is in sight. Dangerous 
heat will build Today into Saturday and continue into Sunday. 
Heat indices will peak on Saturday afternoon, easily exceeding 
100 over southern and especially southeastern areas.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Storms continue to fire along the western edge of cold pool, 
which is currently west of the WC and NW Mountains. Cooler and
more stable air resides across central and north central PA late
this evening with dissipating showers...remnants from earlier
evening deep convection. Keeping slgt chc/chc shra/tsra going
through the early morning hours across much of central and
northern PA, with highest POPs over the west closer to the
deeper convection over far west and northwest PA.

Other than this, all is well on track after minor near term 
tweaks in POPs. The overnight will be very warm and muggy, to
say the least.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
Heat concerns last into Sunday. Saturday should be the hottest
day. But...

There is a real concern for the temps to get as high as curr
fcsts, and therefore, the heat indicies. There is the
possibility of the convective debris/blow-off coming from
upstream on Sat AM to keep the temps down. It is also really
tough to get those 77-79 dewpoints. But, we have hit those
values on Thurs and getting close today (Fri). Will continue all
flags as is with nowhere near enough support to drop/downgrade
any of the flags. PoPs again stay mainly to the north. Warm
temps aloft should limit deep convection and ice production.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
*Heat indexes in from 100 to 110 SE half Sunday afternoon. 
*Excessive heat advisories and warnings through the eastern
 portion of central PA into Sunday. 

The biggest change has been in the pattern for Sunday. The 
front continues to slow and looks to not move through until 
Sunday evening. The upper trough coupled with the low level
frontal boundary pushing into the surface heat dome will kick
off convection Sunday aft that looks to linger into Monday. 
Highs will reach the mid to upper 90s in the SE, with upper 80s
to lower 90s in the NW where clouds will be thicker and
convection more prevalent. But abnormally high dewpoints will
keep the heat oppressive, with heat indexes reaching excessive 
heat warning criteria again Sunday in the SE. 

As the front drops down across the region Monday, a cool down 
is expected. Along with it a break in the oppressive humidity as
the mean upper level trough is nearby. Monday could still be 
muggy over the SE where scattered tstms will continue, but 
overall trend will be that temperatures of 10-20F above normal 
over the weekend will retreat back to near July normals during 
the work week with a mainly dry week in store.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
Not a lot of change for the 06Z TAF package.

Main thing was to add some groups.

Still several areas of showers and storms from northwest PA, 
northwest across Lake Erie, to the upper Great Lakes area.

Overall think these areas will slowly weaken, given that the 
dewpoints and temperatures inland from the Lakes not all that
high, compared to the MDT area. The southeast is too warm aloft
for anything prior to late aft. 

For now, only have VCSH in BFD.

Earlier discussion below.

Fair weather and light wind is expected over most of central Pa
overnight associated with a ridge of high pressure. In those 
portions of northern Pa that received rain this evening, patchy 
fog is possible late tonight. High level cloud debris from 
thunderstorms over the Grt Lks may limit radiational cooling and
fog potential for a while, but expect an increasing chance 
toward dawn Saturday. Model soundings also indicate the
possibility for a period of low mvfr cigs over the Laurel
Highlands (KJST) Saturday morning, resulting from a moist,
upsloping west flow. 

Any morning low cigs or fog should lift by late morning, with 
widespread VFR conditions a near certainty later today. An 
isolated afternoon/evening thunderstorm can't be ruled out, but 
the odds are too low to mention in the forecast at this point. 

.Outlook...

Sun...AM low cigs possible W Mtns. Scattered PM tsra impacts
possible. 

Mon...Widespread showers and tsra impacts possible. 

Tue-Wed...No sig wx expected.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT this evening for PAZ004>006-
010>012-017-018-024-033-037-041-042.
Excessive Heat Warning until 8 PM EDT this evening for PAZ028-
036-046-049>053-056>058-063>065.
Heat Advisory from 8 PM this evening to 8 PM EDT Sunday for 
PAZ028-036-046-049>053-056>058-063>065.
Excessive Heat Warning from noon today to 8 PM EDT this 
evening for PAZ019-025>027-034-035-045.
Heat Advisory until noon EDT today for PAZ019-025>027-034-035-
045.
Excessive Heat Warning until 8 PM EDT Sunday for PAZ059-066.

&&

$$
SYNOPSIS...Dangelo
NEAR TERM...Dangelo/DeVoir
SHORT TERM...Dangelo
LONG TERM...RXR
AVIATION...Fitzgerald/Martin