Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
526 am CDT Friday Aug 1 2014
Short term...(today and tonight)
issued at 345 am CDT Friday Aug 1 2014
Short term concerns remain timing of thunder threat today into this
A weak short wave exiting the eastern County Warning Area early this morning per
water vapor imagery and latest Storm Prediction Center mesoscale analysis. Steep middle
level lapse rates around 7.5 c/km and MUCAPE around 500 j/kg
continue to generate isolated pulse type convection in west
central WI with small hail indicated. This should exit before 12z.
Atmosphere remains ripe for convection to develop ahead of the next
short wave which appears to be moving into far northern Minnesota at this
time. This is prognosticated to drop south and east...and we should see
convection develop into central Minnesota by 15z...and into east central Minnesota
and most of wc Wisconsin around 18z or so. Will mention high chance
probability of precipitation for now...much of this area. Bulk layer shear will be limited
but MUCAPE is prognosticated to increase to around 2k j/kg during the
afternoon...with continued steep middle level lapse rates. Large hail
will be possible with the stronger cells that develop...mainly
across the eastern portion of the area. Maximum temperatures are
expected to warm close to yesterdays values as the trough move
across the region.
This short wave should exit to the south of the area during the
evening with a more diurnal trend in the convection. With general
clearing and light winds...patchy fog will be possible after
midnight across much of the area.
Long term...(saturday through thursday)
issued at 345 am CDT Friday Aug 1 2014
Saturday looks dry with the Friday short wave well to the south.
The next wave to watch will be dropping into Minnesota Saturday
afternoon and evening. This will also be accompanied by shower and
thunderstorm activity...but this activity should not be too
widespread given it/S nocturnal arrival. Coverage may increase a
bit Sunday afternoon as the tail end lingers over eastern Minnesota and western
WI and forecast soundings indicate at least some instability.
Uncertainty has begun to increase again for next week...particularly
for Tuesday and beyond. The European model (ecmwf) had been stable for multiple
runs but the 01.00z edition now features a much deeper trough over
New England and a slightly beefier ridge into south central
Canada. This essentially leads to the stationary front that had
been draped nicely from nodak to central/southern Minnesota and southern WI...to be
positioned further south from sodak to central Iowa and northern Illinois. This
would mean a drier forecast for the majority of the County Warning Area...except
perhaps far southern Minnesota where it could actually be wetter. Not only
does the deeper trough in the northeast result in a further south
frontal position...but it would also delay the main wave from
ejecting eastward as quickly and would result in repeated shower/storm
development through day 7. The GFS ensembles did support a
southward trend to some degree...but not a far south as the European model (ecmwf).
Because this is a very recent development...opted to stay the
course for now and await better continuity with future solutions.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 440 am CDT Friday Aug 1 2014
Initial problem is threat of fog through 13z. Best shot appears
to be at kstc/krnh/Keau with light winds and negligible
temperature/dewpoint spreads. Isolated convection moves southeast of
Keau...but the next short wave is already developing more isolated
convection to the northwest of the area. This is expected to drop
south over the region from mainly 18z-24z. Some rain showers may work into
the northern areas 14z-18z...affecting mainly kaxn. Still should
be isolated so will mention vcsh for now. Will continue to mention
vcsh/prob30 combo at kmsp and tempo into west central Wisconsin.
Still expect activity to wane after 01z with fog possible over
parts of the area after 06z Sat. Did mention that possibility at
kstc/krnh/Keau. Surface winds light through the period...becoming
northwest-north and less than 9 kts through the period.
Kmsp...VFR conditions continue through the period. Some threat of
shra/thunder...after 19z. Will mention prob30 21-23z for now. Then
clearing overnight with light winds. Some possibility of fog...but
low confidence on overall coverage. Light northwest-north winds(less than
9kts) today becoming light south late tonight/Sat morning.
/Outlook for kmsp/
Sat night...VFR. Chance thunderstorms and rain. Winds variable 5 kts.
Sun...VFR. Slight chance thunderstorms and rain. Winds SW 5-10 kts.
Monday...VFR. Chance thunderstorms and rain. Winds SW 5-10 kts.