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Big Heat Week into July 4th Weekend


yoda
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13 hours ago, CAPE said:

@SnowenOutThere

Metrology is important(essential) to meteorology. Not sure that it is taught in a meteorology program(probably not), but imo it probably should be. If not, you can get a more profound understanding of some of the questions you seek by learning a bit more about it. Just a suggestion.

It usually is not. I'm trying to change that here at UMD. I consider myself somewhat of a Meteorologist Metrologist myself. Though I'm always humbled by those NIST people. :lol:

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1 hour ago, Eskimo Joe said:

Interesting low level humidity increase in the mountains. Some dewpoints in the mid 70s already. Hancock mesonet site has a heat index of 99° already. 

Most of the PWS I see around Garrett reporting 85-88 with dewpoints around 70.  90* degree days are pretty rare up there and assuming the next 3 days will be warmer...

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1 minute ago, wxmeddler said:

Thew MD Mesonet station in Frostburg is hovering around a dewpoint of 75-76 degrees with a station pressure of 939.8mb.

That's 21 g/kg Mixing ratio which is CRAZY.

There's gotta be some kind of pooling in the mountains. Even the Poolesville sensor is showing a trend towards higher surface dews and HI.

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2 minutes ago, Eskimo Joe said:

There's gotta be some kind of pooling in the mountains. Even the Poolesville sensor is showing a trend towards higher surface dews and HI.

Definitely an odd mesoscale setup with the old modified arctic airmass sitting off the coast and mixing down the drier air on the eastern shore whole the mountains get obscene moisture 

image.thumb.png.5f663193ebdbef265f6038eb51b2be9e.png

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Detailed analysis in latest NWS Sterling discussion for the upcoming heat wave/ thunderstorm threat.  Nice read with information that hopefully will keep people safe in the upcoming heat wave.

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
345 PM EDT Tue Jun 30 2026

.WHAT HAS CHANGED...
The Heat Advisory for Wednesday has been expanded to include
Calvert and St. Mary`s Counties. The Extreme Heat Watches for
Thursday and Friday have been expanded to include Green,
Albemarle, Nelson, Augusta, and Rockingham Counties. Have
included brief low precipitation chances focused around subtle
boundaries over the next few days.
DISCUSSION...
KEY MESSAGE 1...Extreme heat builds over the region through at
least the end of the week.

What may turn out to be the most intense heat wave since 2012 is
on our doorstep. It is important to plan ahead on how to best
keep safe from the heat.

Have a plan on how to stay cool (and hydrated).

Tips for the heat...
-Keep Cool: If there is not access to air conditioning, you can
 look up nearby cooling centers through local county websites.
 Buildings that do not have air conditioning may remain hot for
 several days after the worst of the heat wave.

-Stay Hydrated: Remember that drinks containing alcohol or
 caffeine actually dehydrate, so balance that with water or
 sports drinks.

-Take It Easy: Try to limit strenuous outdoor activity (work,
 exercise, etc.) to early morning or late evening when it`s not
 as hot.

-Dress For Heat: Wear lightweight, light-colored, loose fitting
 clothing; this helps reflect the sun and allows for airflow to
 keep cooler.

-Look Before You Lock: Never leave anyone unattended in a
 vehicle as temperatures can reach lethal levels in a matter of
 minutes.

-Check In With Each Other: Check in on family, friends, and
 neighbors. The elderly, very young, and those with compromised
 immunity or mental health are at an increased risk from heat.

-Be Aware: Stay tuned to the latest heat alerts and forecast
 from NWS, and be mindful that prolonged extreme heat could
 impact power, water, and transportation systems.

The meteorology...
Low-level moisture has increased substantially with dew points
well into the 70s in the valleys west of I-81. Combined with
widespread air temperatures to around 90, this is resulting in
heat index values of 100 to 105 in the lower elevations of
western MD and eastern WV in the lee of the Appalachian crest.

The heat will continue to build Wednesday as ridging continues
to strengthen just to the south and west. Temperatures soaring
well into the 90s with dew points in the upper 60s (west of the
Blue Ridge) to lower 70s (east of the Blue Ridge) will lead to
heat index values around or a little over 100 (west) and 105
(east) during the afternoon hours. This is covered with a Heat
Advisory for all except the higher elevation zones, although
there is growing concern that prolonged abnormal heat even at
higher elevations could be impactful where there is limited AC
available. Will evaluate as the event draws near to see if those
zones need to be added. In the meantime, have expanded the
advisory into Calvert and St. Mary`s Counties. It looks like the
low-level moisture gets there a bit quicker than in previous
cycles of guidance, possibly aided by slightly higher surface
dew points in the vicinity of the tidal Potomac River and the
Chesapeake Bay.

Extreme Heat Watches remain in effect for Thursday through
Friday when the heat peaks, and have been expanded to include
all but the higher elevation zones (though again concern is
growing for impactful heat even at higher elevations). Air
temperatures are likely to near record values Thursday and
Friday. Dew points will remain elevated especially east of the
Blue Ridge resulting in widespread heat index values well over
100, with increasing potential to exceed 110 east of the Blue
Ridge toward the metros. Areas near larger bodies of water
(tidal Potomac River, Chesapeake Bay) could see spotty heat
indices near 115 at times.

The heat is likely to continue into Saturday, though the exact
magnitude becomes increasingly uncertain several days out. This
uncertainty is also raised due to potential for showers and
thunderstorms that could put a lid on temperatures. Heat
headlines are likely at some point, but confidence in reaching
widespread warning criteria is low for now. Either way, it will
likely be very impactful given it will be several days in a row
of high heat and humidity.

Sunday looks relatively "cooler" though temperatures likely
still reach the 90s with elevated humidity. This could push us
close to Heat Advisory criteria once again.

Even at night, temperatures will stay in the 70s for most
(perhaps not falling below 80 in the major urban centers). This
keeps heat indices in the 90s most of the night, offering
little to no relief from the heat.

Lastly, the intense heat and humidity will likely result in poor
air quality at times. Visit your state`s air quality information
website for more information.


KEY MESSAGE 2...Thunderstorm chance increase through this weekend,
with an increased risk for severe thunderstorms Friday into the
Independence Day weekend.

With excessive heat and humidity comes the potential for severe
weather as abundant instability and moisture pool over the region.

Any showers and thunderstorms through mid week should be very
spotty. A few spots to look out for: near the intersection of a
bay breeze and lee pressure trough Wednesday afternoon, and near
the higher terrain Thursday afternoon. Most of the area/time
will be dry, but any storms that do manage to form could produce
very gusty winds, frequent lightning, and torrential downpours
or even some hail given large amounts of potential energy (CAPE).

Upper-level ridging will gradually buckle Friday before flattening
over the weekend into early next week as the broad subtropical
high pressure shifts further offshore and a series of shortwave
disturbances pivot through. Timing and coverage of storms have
yet to be determined given the placement of synoptic/mesoscale
features. With that said, looking at scattered strong to severe
thunderstorms mainly during the afternoon and evening period
with damaging wind gusts, large hail, heavy rainfall, and
frequent lightning as the main threats. Storms may be of the
pulse variety likely forming along the lee side trough east of
the Alleghenies or residual outflows (i.e the bay/river breeze)
due to the lack shear aloft Friday into Saturday. Of course
this is subject to change based on any ripples of energy that
move between over top of the ridge shunted to the south and the jet
stream to the north (Great Lakes/Ohio River Valley). If this were
to occur, we could be looking at more organized and widespread
storm clusters, but confidence in this is low at this time.

Multiple instances of deterministic/ensemble guidance illustrate
this on both Saturday into Sunday as the ridge flattens further.
Google AI WxNet along with CIPS/CSU AI probs illustrate this
with rather high probabilities of severe weather this weekend.

As we approach the Independence Day weekend, have a weather
preparedness plan ready to go, especially if you are outdoors (i.e
at a picnic with family or a fireworks show). Plan ahead for any
outdoor activities this weekend, as they are likely to be
interrupted by storms at some point. Have a way to get trusted
warnings, download a radar/lightning app to keep aware of changing
weather conditions, and know when to act. When thunder roars, go
indoors. Lightning can strike up to 15 miles outside of the core
of thunderstorms, so wait 30 minutes after that last rumble of
thunder before resuming outdoor activities. Given the heat in
place, some storms could be quite intense (if they form). From a
historical perspective, prolonged near record heat in summer
often ends in a period of strong storms. Intense storms can
produce hail and high winds in addition to rain and lightning,
so having access to sturdy shelter is important.

 

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