Scientific Forecaster Discussion
fxus63 kmpx 262032
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
332 PM CDT Wed Jun 26 2019
Short term...(this evening through Thursday night)
issued at 332 PM CDT Wed Jun 26 2019
The main forecast concern is timing and areal extent of convection
later tonight, and especially Thursday morning as a couple short
waves ride eastward along the periphery of the northern upper level
ridge centered across the mid Mississippi River valley.
Some elevated instability was noted on satellite imagery due to mid
level cloudiness across South Dakota, which was associated with
altocumulus castellanus. This may cause isolated showers/storms to develop in
southwest/west central Minnesota this evening. Otherwise, the main
focus will be a short wave moving across western Nebraska this
evening, and the main short wave moving across the northern rockies.
First, the low level jet should develop and intensify as the short
wave across Nebraska moves eastward this evening. This should allow
for convection to develop in South Dakota, and move eastward into
west central/southwest Minnesota after midnight. As with weather
models, the ec and fv3 have a different scenario of where the
convection develops overnight, and the related convective
vortmax/MCV, and where that translates during the morning/afternoon.
The probability of precipitation is fairly high toward morning in
southwest/west central Minnesota. As the low level jet slowly wanes,
the activity will weaken, but to what extent? This is the first
concern across eastern Minnesota during the morning. However, the
remnants of the morning convection will likely initiate more
activity in the afternoon as the atmosphere destabilizes. Where this
mesoscale convective vortex/convection is located, and where it fires again will be
problematic due to outflow boundaries, cloud cover, etc. The best
scenario is continue high chance percentages with some likely pops
where the the best timing/location of this mesoscale convective vortex/convection should be
in the afternoon. Later forecast will pinpoint a better location of
this mesoscale convective vortex tonight. Severe weather is also related to timing and how
much instability develops in the afternoon. Currently, Storm Prediction Center day 1 & 2
have a good scenario of the best chance of severe weather later
tonight, and tomorrow.
Thursday evening weather will be based on outflow boundaries of
convection that develops Thursday afternoon, and how it translates
in the evening. Precipitable water values are very high later
tonight, and Thursday which will lead to high rainfall rates, and
some localized flooding.
Long term...(friday through wednesday)
issued at 332 PM CDT Wed Jun 26 2019
The hottest weather of the year is set to arrive this weekend, as
a sharp mid/upper-level ridge builds across the central Continental U.S..
The first glimpse at enhanced heat and humidity will be realized
on Friday, as temperatures warm to near 90 and dewpoints increase
into the mid/upper 60s. Even warmer temperatures arrive for
Saturday and Sunday as 925-850mb temps moderate to around +26c.
This should easily translate to highs in the low/mid 90s, possibly
even some upper 90s. Models exhibit good agreement with respect
to these temps. What is less certain is how high dewpoints will
soar, but even the low-end of guidance depicts mid/upper 60s.
Therefore have high confidence that heat headlines will be needed
on Saturday and Sunday. Whether advisory or warnings will be
needed will become more clear as dewpoint trends are more certain.
For wbgt (wet bulb Globe temperature) users, values from 84f-87f
look likely for Saturday and Sunday, possibly even 88f on Saturday
over east central/southeast Minnesota where winds will be fairly light.
While we can't entirely rule out pops over the weekend, more
likely than not we will be too capped for activity, with forecast
700mb temps around +13c. If the ridge does not build in as stoutly
as forecast, we could see showers and thunderstorms similar to
what the European model (ecmwf) depicts for Saturday afternoon/eve with a shortwave
overtopping the building ridge.
The heat looks to abate somewhat on Monday as the northern stream
works to suppress the ridge. There are fairly big differences
between the GFS and European model (ecmwf) regarding how quickly this occurs, but
both models tame temperatures down into the 80s for the first half
of the upcoming week. As this happens, a better opportunity for
shower and thunderstorm chances would return. At this point Sunday
night and Monday look to be a favored time frame, and then
periodic chances continue through the week as the front stalls
along the Minnesota/Iowa border.
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1220 PM CDT Wed Jun 26 2019
The only concern through 00z/28 is whether isolated thunderstorms and rain develop
in central Minnesota where increasing elevated instability
develops by mid/late afternoon. Elsewhere, most of the convection
will hold off until after 06z. The best potential of widespread
convection will occur between 12-18z/28. MVFR cigs/vsbys are a
good possibility along with localized IFR in heavier storms.
Confidence in timing is increasing, however areal coverage remains
problematic due to thunderstorms and rain developing in the Dakotas overnight. These
storms that develop in the Dakotas will be the key on where the
best potential of widespread convection develops toward morning.
Winds will shift to the southeast tonight, and back some as
thunderstorms move across the area Thursday morning.
Timing of any thunderstorms and rain looks to be after 9z, with the best potential
of thunderstorms and rain between 12-16z. MVFR cigs are also a good possibility
once storms develop. Lower confidence on when these storms move
out of the area during the morning/afternoon. Will continue to
trend for VFR in the afternoon with winds becoming southeast
/Outlook for kmsp/
Fri...VFR. Chc thunderstorms and rain early. Winds south-southeast 5-10 kts.
Sat...VFR. Winds S 5-10g15 kts.
Sun...VFR. Chc thunderstorms and rain. South-southwest 5-10 kts.