[SacrydDreamz]

While working my shift this morning (got off at 6am) I noticed the NWS issued a warning with a rapidly decaying thunderstorm on the Eastern Shore of Maryland. Well, interested in what happens today in this area I looked at some obs this morning to get a feel of what we're starting with.

Well, looking at the obs from Salisbury shocked me -- 87F at 2 am? It's real. :scooter:

While not really rare for the plains (though quite uncommon -- there are a handful of observed events every year) it is exceeding rare for the east coast. The attached sounding from Wallops Island, VA will give an idea of what happens.

 WAL__4_26_08_Heat_burst_.gif (39.62K)
Number of downloads: 26
========

As you can se there is a sharp inversion in the surface layer. Well, inversion happen all the time overnight so what makes this special? Well, it the depth of the inversion (shallow), the dry air throughout the sounding and the steep lapse rates above said inversion.

As the thunderstorm decayed in this environment a saturated parcel of air from aloft began to sink and eventually the liquid water content evaporated away. Saturated air will increase at a given rate when it descends, known as the moist adiabatic lapse rate (typically around 6C per km). When the condensed water evaported, the now dry parcel descending and warmed at the dry adiabatic lapse rate, or 9.8C per km.

This is where the steep lapse rate comes into play, because as this occured the parcel remained negatively bouyant -- meanin that while this warming occured on the parcel's descent, the parcel itself remained cooler than the environment and continued to accelerate to the ground. At least until the parcel hit the inversion. At this point the air became warmer than the environment and began to accelerate upward -- in otherwords the rapidly sinking air began to slow down.

Well, the fact that the inversion was so shallow meant that the parcel hit the ground before it could stop its downward motion. AT this point, the parcel was apparently near 90 degrees as observed at SBY! As anticipated, the dewpoint also crashed, falling from the 50s to 41F. Winds also gusted to 52 mph, which is pretty high for a heat burst event, but not unprecedented. Hours later, the temp fell back into the 70s and the dewpoint climbed back into the 50s.

Forecast soundings show a similar environment tonight, so maybe we can catch another!

[dendrite]

Nice catch. Looks like the high was 88F.

[SacrydDreamz]

dendrite, on Apr 26 2009, 09:42 AM, said:

Nice catch. Looks like the high was 88F.

Yeah, would be cool if it stands as the daily high -- but alas, low 90s seem like a good bet.

[dendrite]

SacrydDreamz, on Apr 26 2009, 09:47 AM, said:

Yeah, would be cool if it stands as the daily high -- but alas, low 90s seem like a good bet.

You can see the warming a bit at GED too. Mid 70s to mid 80s and back to mid 70s.

[SacrydDreamz]

dendrite, on Apr 26 2009, 09:49 AM, said:

You can see the warming a bit at GED too. Mid 70s to mid 80s and back to mid 70s.

I saw Annapolis rise from 68 to 77 (but no decrease in Td, interestingly enough)... didn't catch GED. Thanks!

[SacrydDreamz]

Looks to have possibly hit Ocean City between obs... sometime between 3 and 4 am?

[dendrite]

SacrydDreamz, on Apr 26 2009, 09:54 AM, said:

Looks to have possibly hit Ocean City between obs... sometime between 3 and 4 am?

Play around on WU to find some other stations with higher time resolution data. Look at this jump to 86F and 25% RH.

http://www.wundergro...y.asp?ID=MTS530

http://www.wundergro...sp?ID=KDELAURE2

[turtlehurricane]

Thanks for the lesson, cool stuff.

[EastWxWatcher92]

Pin this? This is something that doesn't happen (At least in the MA) often and it'd be a good lesson for those new to the field.

[famartin]

There's a list of cases in Wikipedia:
http://en.wikipedia....wiki/Heat_burst

[ajsaglia]

Here is the culprit for this fascinating event:

[ShoreWXgal]

Pretty cool stuff...Mt Holly made mention of it in their AFD this morning...

http://forecast.weat...p;highlight=off

[Ian]

ShoreWXgal, on Apr 26 2009, 11:18 AM, said:

Pretty cool stuff...Mt Holly made mention of it in their AFD this morning...

http://forecast.weat...p;highlight=off

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
421 AM EDT SUN APR 26 2009

OVERNIGHT HOURS PROVED TO BE EVENTFUL FOR THE MD ERN SHORE AS A DECAYING THUNDERSTORM CROSSED CHESAPEAKE BAY AND ENTERED NW DORCHESTER COUNTY SHORTLY AFTER MIDNIGHT. THIS FEATURE APPEARED TO WEAKEN FURTHER...AND IT EVENTUALLY WAS PRODUCING LITTLE IF ANY PRECIPITATION (AND NO LIGHTNING WAS DETECTED)...WHILE CONTINUING TO MOVE SLOWLY SE AS A WEAK BNDRY BETWEEN 1 AND 2 AM THIS MORNING. HOWEVER...OBSERVATIONS AT KCGE REPORTED A WIND GUST TO 35 KT AROUND MIDNIGHT...AND AT POWELLVILLE A GUST TO 30 KT...AND MOST NOTABLY KSBY AT 2 AM REPORTED A SUSTAINED WIND OF 33 KT W/ A GUST TO 45 KT...IN ADDITION TO A SHARP INCREASE IN TEMP TO 88 DEG AND A PLUMMETING DEW PT OF 41! ALL SIGNS POINT TO HEAT BURST...WHICH IS QUITE RARE FOR THIS AREA. THIS FEATURE APPEARS TO HAVE FINALLY DISSIPATED UPON REACHING THE MD COAST BTWN 330 AND 4 AM THIS MORNING.


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
506 AM EDT SUN APR 26 2009

BY THE WAY, WE`LL START OFF RATHER WARM IN THE FAR SOUTHERN ZONES BECAUSE OF WHAT OUR COLLEAGUES IN WAKEFIELD NOTED WAS A HEAT BURST OVERNIGHT. TEMPERATURES AT ONE POINT EARLY THIS MORNING HAD RISEN TO 85 DEGREES AT GED.

Quote

svrakq
mdc039 - 045 - 047 - 260700-
/o. new. kakq. ******. w. 0045. 090426t0606z - 090426t0700z/

bulletin - eas activation requested
severe thunderstorm warning
national weather service wakefield va
206 am edt sun apr 26 2009

the national weather service in wakefield has issued a

* severe thunderstorm warning for...
northeastern somerset county in southeast maryland...
eastern wicomico county in southeast maryland...
worcester county in southeast maryland...

* until 300 am edt

* at 203 am edt ... national weather service doppler radar indicated a
line of severe thunderstorms capable of producing damaging winds in
excess of 60 mph. these storms were located along a line extending
from parsonsburg to 8 miles south of parsonsburg to pocomoke
city ... or along a line extending from 10 miles northeast of
salisbury to 8 miles southeast of fruitland to pocomoke
city ... and moving southeast at 10 mph.

* severe thunderstorms will be near...
pocomoke city by 225 am edt...
snow hill ... 7 miles west of newark and 9 miles west of berlin by
240 am edt...

lat ... lon 3814 7516 3802 7526 3803 7527 3823 7516
3820 7520 3824 7522 3808 7528 3807 7529
3807 7530 3809 7529 3809 7533 3804 7532
3802 7537 3806 7574 3829 7559 3846 7556
3845 7504
time ... mot ... loc 0606z 294deg 4kt 3845 7542 3827 7549
3814 7560

$$

brown

[North MD]

Very interesting Randy. I have never heard of this or can recall anything like this before.

[SacrydDreamz]

North MD, on Apr 26 2009, 12:07 PM, said:

Very interesting Randy. I have never heard of this or can recall anything like this before.

It happens in the Plains every year at least a handful of time... usually in the Dakotas or Nebraska. This is the first time I can recall it on the East Coast -- but then again I have not been looking very long :)

[dan11295]

Last year in one night there was a heat burst in Sioux Falls, SD where the temp rose to 99F (which ended up being logged as the daily high for that station)

[SacrydDreamz]

Ian, on Apr 26 2009, 11:41 AM, said:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WAKEFIELD VA
421 AM EDT SUN APR 26 2009

OVERNIGHT HOURS PROVED TO BE EVENTFUL FOR THE MD ERN SHORE AS A DECAYING THUNDERSTORM CROSSED CHESAPEAKE BAY AND ENTERED NW DORCHESTER COUNTY SHORTLY AFTER MIDNIGHT. THIS FEATURE APPEARED TO WEAKEN FURTHER...AND IT EVENTUALLY WAS PRODUCING LITTLE IF ANY PRECIPITATION (AND NO LIGHTNING WAS DETECTED)...WHILE CONTINUING TO MOVE SLOWLY SE AS A WEAK BNDRY BETWEEN 1 AND 2 AM THIS MORNING. HOWEVER...OBSERVATIONS AT KCGE REPORTED A WIND GUST TO 35 KT AROUND MIDNIGHT...AND AT POWELLVILLE A GUST TO 30 KT...AND MOST NOTABLY KSBY AT 2 AM REPORTED A SUSTAINED WIND OF 33 KT W/ A GUST TO 45 KT...IN ADDITION TO A SHARP INCREASE IN TEMP TO 88 DEG AND A PLUMMETING DEW PT OF 41! ALL SIGNS POINT TO HEAT BURST...WHICH IS QUITE RARE FOR THIS AREA. THIS FEATURE APPEARS TO HAVE FINALLY DISSIPATED UPON REACHING THE MD COAST BTWN 330 AND 4 AM THIS MORNING.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
506 AM EDT SUN APR 26 2009

BY THE WAY, WE`LL START OFF RATHER WARM IN THE FAR SOUTHERN ZONES BECAUSE OF WHAT OUR COLLEAGUES IN WAKEFIELD NOTED WAS A HEAT BURST OVERNIGHT. TEMPERATURES AT ONE POINT EARLY THIS MORNING HAD RISEN TO 85 DEGREES AT GED.

No thunder, then it wasn't a thunderstorm :devilsmiley:

[SacrydDreamz]

dan11295, on Apr 26 2009, 12:17 PM, said:

Last year in one night there was a heat burst in Sioux Falls, SD where the temp rose to 99F (which ended up being logged as the daily high for that station)

I recall that -- I did a paper in college on a heat burst event in Sioux Falls. But that event was back in the late 90's I believe.

[A-L-E-X]

Hmmm, is this the reason why JFK was in the mid 80s in the early morning hours as well? We were +25 from yesterday!

[Ian]

SacrydDreamz, on Apr 26 2009, 12:23 PM, said:

No thunder, then it wasn't a thunderstorm :devilsmiley:

severe shower warning doesnt have the same ring i guess