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Area Forecast Discussion (AFD)

Issued by State College, PA (CTP)

FXUS61 KCTP 200228

Area Forecast Discussion
National Weather Service State College PA
1028 PM EDT Fri Jul 19 2019

----Dangerous heat and humidity expected today 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.


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.


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.


*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.


A dying band of thunderstorms over west central Pa at 0045Z 
should continue to dissipate as the sun sets this evening with 
no significant impacts at the central Pa TAF sites. 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. 

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


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

Mon...Widespread showers and tsra impacts possible. 

Tue-Wed...No sig wx expected.


Heat Advisory until 8 PM EDT Saturday for PAZ004>006-010>012-
Excessive Heat Warning until 8 PM EDT Saturday for PAZ028-036-
Heat Advisory from 8 PM Saturday to 8 PM EDT Sunday for PAZ028-
Excessive Heat Warning from noon to 8 PM EDT Saturday for 
Heat Advisory until noon EDT Saturday for PAZ019-025>027-034-
Excessive Heat Warning until 8 PM EDT Sunday for PAZ059-066.


NEAR TERM...Dangelo/DeVoir
SHORT TERM...Dangelo