Scientific Forecaster Discussion
fxus63 kmpx 152312
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
612 PM CDT Mon Jul 15 2019
Updated for 00z taf discussion below...
Short term...(this evening through Tuesday night)
issued at 315 PM CDT Mon Jul 15 2019
Two separate mechanisms for producing thunderstorms are present this
afternoon across the upper Midwest. In addition, heat indices have
been hovering from 95-100 degrees generally, with a few sites
eclipsing 100 with locally higher dew point readings.
The first mechanism for storms is the mesoscale convective vortex moving east across far
southeastern Minnesota with thunderstorms to the north of the mesoscale convective vortex
(similarly to yesterday) that are expected to remain sub-severe.
Instability and shear are limited there so expect main issues to be
lightning, small hail, heavy downpours mainly through about 5pm.
The severe weather threat this afternoon and evening is tied to the
approaching frontal boundary to our northwest. The uncertainty that
remains is just how far south will convection break through the cap
along the front. Latest thinking is storms will affect central Minnesota,
north of St. Cloud this afternoon, but expansion southward is not
likely during the afternoon. Hence, expect most of our local
thunderstorm development after 00z once the atmosphere begins to
cool. Storms will likely move southeast but hi-res cams continue to
show discrepancies in coverage. MLCAPE values of 2,500-3,500 j/kg
with near 30 knots of effective shear will be ample to produce large
hail and severe wind gusts with the stronger storms. A Severe
Thunderstorm Watch was issued along and north of a line from near
Alexandria through St. Cloud and Ladysmith, WI. To the south of this
area, the storm threat would occur later so plenty of time to
monitor trends and could expand the watch or issue a new watch if
needed. At this point though, think it may evolve into more of a
heavy rainfall threat by that time after dark. Could see isolated 2-
4" of rainfall given slow moving thunderstorm potential tonight.
Additional thunderstorms will be possible tomorrow as the
aforementioned frontal boundary essentially stalls out across the
area. Tomorrow doesn't look quite as hot as today and severe storm
potential marginally less, but as per usual with summertime
convection with a moist and unstable airmass, uncertainty in timing
and intensity of storms is somewhat high at this time.
Long term...(wednesday through monday)
issued at 315 PM CDT Mon Jul 15 2019
Longer term concerns remain heat/humidity and timing of convection
through the remainder of the week.
At the beginning of the period, models indicate a rather vigorous
short wave trough moving through the Dakotas/Minnesota region
Wednesday/Wednesday night. This should bring likely chance pops
over the northern and eastern portion of the County Warning Area during this
period. Severe weather threat will remain depending on overall
heating/destabilization. Along with the severe weather threat,
heavy rainfall will also be possible with naefs pw's indicating
2-3 Standard deviations above normal.
Model trends continue to indicate heat/humidity concerns
returning Thursday or Friday after this initial wave. Both the
European model (ecmwf) and GFS bring the nearly stationary frontal boundary into
about the southern third of Minnesota. South of the front we
should see very warm air with the European model (ecmwf) particularly warm. North
of the front, we may be susceptible to periodic strong convection.
This will likely continue into Saturday before a stronger
trough/cold front moves across the region Sunday/Monday. At the
moment, we have trended high temperatures more to the 75
percentile of the member envelope into Saturday, which was
generally a degree or two warmer than nbm.
Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 630 PM CDT Mon Jul 15 2019
Convection dropping slowly east/southeast should ahead of weak
surface front/boundary. Convection did generate several outflows
in and around central/east central Minnesota and may remain a factor for
a few hours yet. Otherwise, main area of convection should drop
south and gradually weaken with time, affecting Keau/kmkt before
05z. Otherwise, continue chance of MVFR fog most areas and MVFR
cigs/fog over wc WI. Should clear out early Tue morning. Timing of
next bout of possible trsa looks to be after 18z Tuesday.
Kmsp...aww issued earlier. Convection should exit the area
through 02z or so. Then may see some light fog develop late with
next chance of thunder returning after 21z Tuesday.
/Outlook for kmsp/
Wed...mainly VFR. Thunderstorms and rain likely. Winds S 5 kts.
Thu...mainly VFR. Possible thunderstorms and rain late. Winds light and variable.
Fri...VFR. Winds light and variable.
Minnesota...heat advisory until 10 PM CDT this evening for mnz060>063-