Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Sun May 15 2022

Valid 00Z Mon May 16 2022 - 00Z Wed May 18 2022

...Severe weather and flash flooding potential across the Lower
Mississippi/Ohio Valley tonight to shift into the Northeast on Monday...

...Next system to eject into the Great Plains on Tuesday to produce
another potential round of severe weather from the central Plains to the
Mid-Mississippi Valley...

...Summer-like and record breaking heat to persist across Southwest and
southern Plains through the beginning of the week...

Spring has kicked into full gear across the country, with daily chances
for severe thunderstorms and flash flooding as well as widespread
summer-like temperatures. A cold front progressing across the Ohio Valley
and into the southern Plains will trigger a continuing severe weather
threat into tonight. Thunderstorms will be capable of producing damaging
wind gusts, large hail, and tornadoes from eastern Oklahoma to northern
Arkansas and southern Missouri. Torrential rain may also accompany the
storms and lead to isolated instances of flash flooding. A few
thunderstorms could turn severe farther east into the Ohio Valley as well.
By Monday, a rapidly strengthening low pressure system along the
aforementioned cold front will swing eastward and eventually into the
Interior Northeast. As it does so, a line of potentially severe
thunderstorms is expected to develop ahead of the approaching cold front
and impact parts of the Northeast and Mid-Atlantic. Damaging wind gusts
and isolated tornadoes are the main concern, with large hail also
possible. The Storm Prediction Center has issued an Enhanced Risk (level
3/5) of severe thunderstorms from Upstate New York to northern Virginia.
Additionally, flash flooding may accompany any slow-moving thunderstorms
for this region, with a slightly more elevated heavy rain threat located
in northern New York and Vermont, where a Slight Risk (level 2/4) for
excessive rainfall has been issued. The strong spring cold front will exit
into the western Atlantic by Monday night, ushering in comfortable
temperatures and increasingly tranquil conditions for the region on
Tuesday.

The next system to impact the central U.S. will eject into the Great
Plains by Tuesday. Areas of low pressure forming in the lee of the Rockies
will slowly push eastward and interact with a nearby stationary front to
focus showers and thunderstorms across the central Plains. SPC has issued
an Slight Risk (level 2/5) of severe thunderstorms across southern
Nebraska, northern Kansas, and into parts of Iowa and Missouri. Torrential
downpours and isolated chances for flash flooding may also accompany the
storms.

Elsewhere, unsettled weather located across the Northwest could spawn
scattered severe thunderstorms throughout the Interior Pacific Northwest
tonight. Terrain susceptible to rapid runoff will also be under the risk
of flash flooding, which has prompted Flood Watches to be issued. For the
Southeast and Deep South, a warm and muggy airmass ahead of the
approaching cold front will produce an environment conducive for scattered
showers and thunderstorms over the next few days, with most storms
remaining unorganized and short-lived. However, an isolated severe storm
or two cannot be ruled out.

Outside of the Northwest, Great Lakes, and Upper Midwest, above average
temperatures will be widespread over the next few days and could reach
into record territory for portions of the southern tier. Highs into the
upper 90s and triple digits are forecast across the Desert Southwest and
southern Plains through Tuesday. Particularly for the Lone Star State,
highs nearly 20 degrees above average on Tuesday will have the potential
to break several daily high temperature records. The continuing
early-season heat can be dangerous is proper heat safety is not followed.
Residents are urged to stay hydrated and avoid strenuous outdoor
activities during peak heating hours.

Snell

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Sun May 15 2022

Valid 12Z Wed May 18 2022 - 12Z Sun May 22 2022

...Persistent record-breaking heat is likely in the south-central
U.S. through this week with anomalous heat expanding into the East
by the weekend...


...Overview...

Upper troughing should shift out of the Northeast as the period
begins on Wednesday, with broad ridging to zonal flow behind
across the rest of the lower 48. The pattern is expected to
amplify later in the week as upper troughing digs in the West,
yielding cooler temperatures and lowering snow levels in a round
of precipitation spreading across the Northwest. Stubborn ridging
across the South will continue to promote unseasonably hot
weather, with the most persistent and record-breaking heat
centered in Texas and the Lower Mississippi Valley. Warmer than
normal temperatures are forecast to spread into the East as the
ridge amplifies ahead of the trough in the West, but the heat
should finally break by next weekend across parts of the South.
Initially the best focus for showers and thunderstorms around
midweek will be over the Ohio Valley along a quasi-stationary
front, before precipitation spreads into the north-central U.S.
around Thursday and eastward late week. Flash flooding and severe
weather are both threats with this system. Shower/thunderstorm
chances will also increase in Florida late this week given
increasing tropical moisture.


...Guidance Evaluation/Preferences...

Model guidance remains in good agreement for generally zonal flow
with a couple of embedded shortwaves across the lower 48 to start
the medium range period Wednesday, before amplification later this
week as troughing builds in the West creating ridging downstream.
The process for building this trough stems from potent energy
initially just offshore of British Columbia spilling into the
Northwest late Wednesday into Thursday and progressing eastward.
However, some notable differences remain regarding the splitting
of this energy into multiple features or more consolidation, as
well as variation with an embedded upper low being closed at
different points/times. Recent model guidance including some of
the 00Z runs and the newer 12Z runs have trended toward showing a
closed low around Friday, separate from but eventually interacting
with a farther north Hudson Bay upper low. Namely, the 00Z/12Z
ECMWF and UKMET indicated a closed low, while the 12Z GFS and CMC
trended toward this as well after more open earlier runs. 12Z runs
are thus showing better agreement for the surface low position as
well in the Upper Midwest day 5/Friday, so hopefully frontal
positions and QPF are following suit. The southern end of the
trough's progression remains somewhat uncertain as does the
eastern side by around Saturday, with the latter issue dependent
on interactions with that northern stream low. There has been a
gradual trend toward a slower trough and thus frontal progression
in the northeastern U.S. compared to previous forecasts. The 00Z
CMC appeared to be on the faster side. The updated WPC forecast
used a blend of the 00Z/06Z deterministic guidance early in the
period, transitioning toward a near even blend of the
GFS/ECMWF/GEFS mean/EC mean by the latter part of the period.


...Weather/Threat Highlights...

Initial ridging across the southern Plains and rising heights
farther east over the Deep South will promote a broad area of heat
across much of the southern U.S. during the period. The greatest
and most lasting anomalies through the period should be over Texas
(persisting from the short range time frame) where some locations
could see highs up to 15-25F above normal, with numerous daily
record highs likely. Parts of the Southwest into the central Great
Basin and southern/central Rockies can expect highs around 10F
above average on Wednesday before a cooling trend as the deeper
troughing presses inland, which should help moderate temperatures
in Texas by the weekend. However, warm to hot temperatures are
also forecast for the southeastern quadrant of the U.S. with
potential for daily record highs, and warmer than average
temperatures by 10-20F should expand in coverage across the Ohio
Valley to Eastern Seaboard by later in the week.

A warm front lifting through the Mid-Mississippi Valley and Ohio
Valley will provide a focus for multiple areas of showers and
storms/convective complexes during the middle to latter part of
the week. The ingredients are in place for heavy rainfall, though
the specifics of coverage and amounts are uncertain, but at least
a localized flood threat is likely especially if heavy rain falls
in areas that are sensitive to additional rainfall. Then organized
rainfall, heavy at times, is likely along a frontal boundary
through the north-central U.S. around Thursday with potential for
at least localized flood and flash flood threats given wet
antecedent conditions across that region. Storms that could be
severe are forecast to shift from the Upper Midwest into parts of
the Ohio and Mississippi Valleys along this front Thursday into
Friday. Additionally, tropical moisture increasing across the
Florida peninsula late this week could lead to a more rainy
pattern for the Sunshine State.

After a couple of initial fronts crossing the Northwest, the main
well-defined front ahead of the deepening trough will bring
unseasonably cool temperatures to the Northwest and expanding into
the northern Rockies and High Plains by late week. This will also
provide support for a notable round of precipitation, with
lowering snow levels in the Cascades to Northern Rockies as the
week progresses, with some chance of snow even into northern parts
of the High Plains, though with very low confidence at this point.


Tate/Santorelli