Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
329 PM CDT Wednesday Jul 23 2014
Short term...(this evening through thursday)
issued at 309 PM CDT Wednesday Jul 23 2014
Near normal temperatures and a mostly dry forecast is still expected
in the short term with the exception of thunderstorm potential
from west central to south central Minnesota tomorrow morning.
The regional radar scope is quiet this afternoon with all the
convective activity either tied to the cold front across the
eastern Great Lakes...Ohio River valley and middle Mississippi River or
on the east side of the upper ridge embedded in the anticyclonically
rotating moisture plume and thickness diffluence in Kansas and NE. The
surface high is building across the area this afternoon...but this
high should weaken and slide east tonight. The low level jet quickly
strengthens this evening over the High Plains and the result will be
Theta-E advection into the eastern Dakotas and far western Minnesota by
sunrise tomorrow morning. The 23.12z NAM/GFS/Gem and most of the
available cam guidance from last night and this morning want to
drive any convection that forms on the nose of the low level jet south with
time and weaken the activity before it penetrates too far into
Minnesota. This would mean most of the area would remain dry
tomorrow /at least during the daylight hours/. The 23.00z European model (ecmwf) was a
bit of an outlier with the western extent of the precipitation during the
day tomorrow...the 23.12z is a little slower than its 00z
counterpart but it would still suggest chance-to-likely probability of precipitation in west
central Minnesota between 18-00z.
Long term...(thursday night through wednesday)
issued at 309 PM CDT Wednesday Jul 23 2014
The main theme for the extended period is a change from an unsettled
pattern at the beginning...to a more late Summer type pattern
with drier and cooler than normal weather scenario by next week.
Thursday night/early Friday morning will remain problematic in
terms of where the nocturnal low level jet will develop and veer during the
morning hours...which will translate to higher probability of precipitation and quantitative precipitation forecast amts in
the region. Current models indicate that the nose of the low level jet will
develop somewhere in southern Minnesota/northern Iowa Thursday
evening...with winds veering more west/west-southwest by Friday
morning...changing the maximum convergence in the low levels
across Iowa by Friday morning. Best chance/S of rainfall will occur
during this time frame...especially where the best convergence
along this low level jet remains.
After Friday morning...a surface trough will move across Minnesota/western WI
leading to some afternoon/evening shra/tsra. Best chance/S will occur late
Saturday/Sunday as the main upper low that is currently moving
into the Pacific northwest this afternoon...moves along the Canadian border
tracking some upper level energy eastward along this fast moving
west to east flow aloft Fri/Sat.
Once this feature along the Canadian border moves east of Minnesota and
begins to dig south/southeast across the eastern U.S. Our weather will turn
cooler than normal. In addition...N/NW flow aloft will mean a
drier pattern with most of the action along the Gulf Coast states
and eastern U.S.
This transition to a cooler pattern will likely continue through the
beginning of August as a strong upper ridge anomaly is currently
advertise in the extended models building off the eastern coast of
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1157 am CDT Wednesday Jul 23 2014
Outside of common clear skies - light wind fog at kstc/krnh/Keau
tomorrow morning for a a couple hours...look for VFR conditions
and an overall dry set of tafs. We do expect a batch of showers
and weak thunderstorms to form in the eastern Dakotas and move
into west central and southwest Minnesota tomorrow morning...but most of
the activity should stay west of the taf sites. The exception
could be krwf...which appears close enough to get some rain. It
appears the activity will remain farther west than previous
though...but later shifts will monitor the eastern extend of the
rain and add it to sites if needed. Thursday night looks a little
better for rain at the rest of the Minnesota taf sites.
No aviation weather concerns in the short term with clouds that
have VFR bases. We'll have to keep an eye out for the Thursday
evening commute if some of the thunderstorms that are likely in
western Minnesota start to translate farther east than expected.
/Outlook for kmsp/
Thursday night...VFR. Chance MVFR conds west/ thunderstorms and rain overnight. Winds southeast at
Friday...VFR. Chance thunderstorms and rain. Winds south-southeast at 5-10kts.
Sat...VFR. Winds west at 10kts.