June 3rd, 2020 Derecho

Area Forecast Discussion

Area Forecast Discussion

578 

FXUS61 KCTP 030858

AFDCTP

Area Forecast Discussion

National Weather Service State College PA

458 AM EDT Wed Jun 3 2020

.SYNOPSIS...

Potentially strong thunderstorms are expected today and into 

the evening as a frontal boundary slides southward through the

state. It will remain unsettled Thursday into Friday, and 

possibly right into the weekend. High pressure and dry air take

hold Sunday and lasts into Tuesday. 

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Earlier strong/severe storms have dropped into the lower Susq

valley and continue southward. While they have weakened, some of

the cells are still potent. They continue to move into less-

favorable air, esp at the sfc. This convection seems to be more

aloft than sfc-based. They should continue to weaken. 

Eyes turn to the large storms moving over LE from Lower ONT.

These are on track to reach Warren Co around 6 AM. Will see what

the lake water/temps and dewpoints do to them. This convection

is a little faster than what model solutions have going. This

would have repercussions on the going fcst, perhaps resulting 

in the storms being less potent if the heating of the day does 

not have as much time to occur before the storms reach the 

NC/NErn counties. However, the latest HRRR does develop a new 

batch of storms back to the west of this stuff, and moves it 

across in the current timing of the forecast. This is in line 

with the most notable short wave trough we see in this fast WNW 

flow. So, will hold the line for the time being on all timing, 

but add in the mention of stronger storms arriving a little 

quicker in the NW.

Storm attributes/mode appear to be supercellular at first, but

then would morph into clusters/bowing segments. Bulk shear is

50-60kts with the mid-levels holding 60kt westerly winds which,

on a uni-direction shear day like today, will efficiently mix 

down and producing long-lived bow echoes. Lingering boundaries

from overnight convection will make plenty of places to generate

storms. The early-day timing across the north is a slight

detriment to severe potential.

Some sunshine and heating is expected in the SW, and the main

boundary for storms to focus upon will create locations in the

central and SWrn counties for development this aftn. The

coverage over the Lower Susq and S-Central mtns is expected to

be lower, but the atmos is still potent there. There may be

CAPEs in the 2000 range in the SE, but high cloud coverage from

upstream convection could knock that down. Shear is also around

40KTs there, lower than inn the north. It is only a couple of 

times a year that Central PA is placed into a ENH risk, so we 

need to be attentive to any cells that develop. 

Temps will be a function of the clearing we get and how early

the storms occur in the north. Maxes should get into the 80s in

the south, but only the lower 70s along the NY border. Wind will

probably be gusting into the 20s over the SW/SC before the

storms flare up there. 

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...

Storms should still be going early this evening in the southern

third of the area, but clearing should be starting across the 

north. This clearing may self-destruct and turn to some fog, but

if the clearing occurs earlier in the aftn, it could dry out 

well enough to keep fog patchy. Low clouds are also possible

where the wind is an upslope (Alleghenies). Storms/showers will

diminish for everyone but the SW around or shortly after

midnight. Sticky air will keep the temps from falling out of the

mid 60s for about half of the area. With some clearing, the nrn

mtns could get into the 50s. 

The old boundary will likely be along the srn border Thurs 

morning, the sfc wind will be light and SWrly. Upper flow 

flattens to a W-E direction, and lingering moisture and daytime 

heat will lead to showers and storms in the aftn. The shear will

be lacking, but CAPEs could reach 1000 or better across the

south. So, a few of the storms could go severe, but most likely,

without the shear, many will be sub-severe. SPC MRGL risk is

enough to keep a close eye on them. Maxes Thurs will be just as

warm across the north than the south, thanks to more sun up

north. The coolest place will be the Laurels where clouds and a

higher chc of showers exist. 

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...

The old front will stall near the PA-MD border on Thu, keeping 

a chance of rain showers and maybe a few PM tstms through Fri. 

Generally a quarter to half an inch of rain is expected across 

the southern counties Thu-Fri, with locally higher amounts in 

storms. Lesser amounts north.

The stationary front is progged to move offshore Fri night, with

slightly drier air moving in for Sat. Another cold front and 

shortwave trough may touch off isolated showers/storms Sat, but

drier air will be a limiting factor. Cooler, drier air will move

in behind this front for Sun-Mon. We will see a warming trend

into the middle of next week as the remnants of TS Cristobal

moving up the MS valley help build an upper ridge over the

eastern US.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...

Multiple rounds of showers and t-storms will move across parts

of the airspace from early this morning through early tonight.

Confidence in exact timing/details is still somewhat uncertain,

but the general storm evolution seemed to be handled reasonably

well by the hires models. The first cluster of storms will 

continue to slide southeast and impact airfields near and east 

of a line from KOYM/KUNV/KMDT. The second round of storms should

be associated with t-storm complex currently moving across srn 

MI which is fcst to translate downstream through srn Ontario and

across Lake Erie later this morning. Model guidance tracks this

feature which /may be accompanied by severe wind gusts/ east- 

southeast across north central PA into eastern PA btwn 13-19Z. 

The third and final round of t-storms should form along a 

southeastward advancing cold front and impact the south central 

airspace later this afternoon into early tonight. Outside of

t-storms, expect mainly VFR conditions to prevail during the

03/06Z TAF period. 

Outlook...

Thu...Showers/t-storms likely especially srn 1/2. 

Fri-Sat...Chance of showers/t-storms. 

Sun...VFR/no sig wx.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...

None.

&&

$$

SYNOPSIS...Dangelo/Evanego

NEAR TERM...Dangelo

SHORT TERM...Dangelo/Evanego

LONG TERM...Gartner/Colbert

AVIATION...Steinbugl

Storm Reports

523 

NOUS41 KPHI 031851

PNSPHI

DEZ001>004-MDZ008-012-015-019-020-NJZ001-007>010-012>027-PAZ054-055-060>062-

070-071-101>106-040651-

Public Information Statement

National Weather Service Mount Holly NJ

251 PM EDT Wed Jun 3 2020

...HIGHEST THUNDERSTORM WIND GUST REPORTS...

Location                     Speed     Time/Date       Provider             

...New Jersey...

...Burlington County...

2 SE Jacksonville            67 MPH    1240 PM 06/03   Mesonet              

1 NW Rancocas                65 MPH    1230 PM 06/03   NWS Employee         

2 SW Rancocas                65 MPH    1235 PM 06/03   Mesonet              

1 ESE Lumberton Twp          61 MPH    1240 PM 06/03   Mesonet              

1 SE Lumberton               60 MPH    1240 PM 06/03   Trained Spotter      

...Camden County...

1 SSW Palmyra                59 MPH    1230 PM 06/03   Mesonet              

...Mercer County...

Trenton Mercer Airport (KTTN 58 MPH    1232 PM 06/03   ASOS                 

...Monmouth County...

1 ESE Brielle                76 MPH    0114 PM 06/03   Public               

...Ocean County...

2 SW Beach Haven             89 MPH    0115 PM 06/03   Mesonet              

Brick                        87 MPH    0114 PM 06/03   Mesonet              

Harvey Cedars                70 MPH    0115 PM 06/03   Mesonet              

4 SE Mystic Island           68 MPH    0118 PM 06/03   Mesonet              

5 SE Mystic Island           68 MPH    0118 PM 06/03   Mesonet              

Berkeley Twp                 67 MPH    0105 PM 06/03   Mesonet              

Lakehurst Maxfield Field Air 66 MPH    1258 PM 06/03   AWOS                 

4 SE Mystic Island           66 MPH    0110 PM 06/03   Mesonet              

Seaside Park                 63 MPH    0108 PM 06/03   Mesonet              

2 SSW Seaside Park           63 MPH    0115 PM 06/03   Public               

3 W Jackson                  59 MPH    0100 PM 06/03   Mesonet              

Ocean County Airport (KMJX)  59 MPH    0102 PM 06/03   AWOS                 

1 ENE Lanoka Harbor          59 MPH    0112 PM 06/03   Mesonet              

1 NNE Surf City              59 MPH    0115 PM 06/03   Public               

...Pennsylvania...

...Berks County...

Reading Regional Airport (KR 83 MPH    1135 AM 06/03   ASOS                 

Reading Regional Airport (KR 67 MPH    1134 AM 06/03   ASOS                 

1 SSW Ruscombmanor Twp       60 MPH    1145 AM 06/03   Mesonet              

...Bucks County...

1 SSW Bristol                64 MPH    1230 PM 06/03   Mesonet              

...Chester County...

Malvern                      75 MPH    1215 PM 06/03   Public               

North Coventry Twp           67 MPH    1156 AM 06/03   Trained Spotter      

...Delaware County...

1 W Philadelphia Intl        59 MPH    1229 PM 06/03   Other Federal        

...Montgomery County...

Pottstown                    76 MPH    1159 AM 06/03   Trained Spotter      

1 SSE Fort Washington        66 MPH    1225 PM 06/03   Mesonet              

...Philadelphia County...

1 E Holmesburg               71 MPH    1230 PM 06/03   Mesonet              

Northeast Philadelphia Airpo 68 MPH    1225 PM 06/03   ASOS                 

Philadelphia International A 61 MPH    1228 PM 06/03   ASOS                 

...New Jersey...

...Maritime Stations...

2 E Waretown                 72 MPH    0113 PM 06/03   Mesonet              

1 E Barnegat Light           69 MPH    0114 PM 06/03   Mesonet              

2 WSW Ship Bottom            68 MPH    0115 PM 06/03   Mesonet              

2 SSW Seaside Park           66 MPH    0113 PM 06/03   Mesonet              

Barnegat Light               60 MPH    0118 PM 06/03   Mesonet              

&&

Environment

Upper-level maps

250-mb Analysis 6/3/20 12Z	500-mb Analysis 6/3/20 12Z

Surface Maps

Surface Map 6/3/20 12Z	Surface Map 6/3/20 21Z

Sounding Data

12Z Pittsburgh, PA Sounding	0Z PIttsburgh, PA Sounding

SPC Data

SPC Filtered Reports for 06/30/2020	SPC Day 1 Outlook and Preliminary Reports 06/30/2020