Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
541 am CDT Wednesday may 6 2015
Updated for 12z aviation discussion below...
Short term...(today and tonight)
issued at 410 am CDT Wednesday may 6 2015
The short term concerns are fog this morning...timing and extent of
convection and temperatures.
Dense fog along the Minnesota/Iowa border this morning...ahead of warm font
over Iowa. The stratus and fog are expected to remain through at
least middle morning...then lifting thereafter. The most dense fog
will affect the southern two tier of counties and an advisory was
issued around midnight for this.
The band of showers developed from the metropolitan east into Wisconsin
overnight and should exit there by around 12z. Other
showers/isolated thunder lifting north/northwest across central
Iowa...and will affect mainly western areas through the morning.
Will hold onto higher probability of precipitation to the west and north with some lower
probability of precipitation/slight chance developing into western Wisconsin through the
morning. Clouds will hold firm much of the day...perhaps breaking
out some during the afternoon. Dewpoints expected to remain close
to 60f which will feel a bit muggy. Temperatures should warm
through the 70s...but could warm to 80 if the sun breaks out into
the afternoon in the southwest.
Water vapor imagery showing next strong wave over Oklahoma/Kansas
region...which will lift northeast toward Iowa by late afternoon.
Should see shower/thunder increase from west to east during the
aternoon. Then activity should wane into the late evening before
the brunt of the upper trough moves into the area later tonight.
This will spread likely/categorical probability of precipitation east once again through 12z
Thursday. The severe weather threat is conditional at best...with the
amount of cloud cover/limited heating expected.
Long term...(thursday through tuesday)
issued at 410 am CDT Wednesday may 6 2015
The short term addresses the precipitation late tonight with a pronounced
low level jet and strong moisture transport. In fact...there is really good
consensus among the NAM/GFS/ECMWF of a 40-50kt jet nosing into
Minnesota/WI by sunrise Thursday morning. This will allow the warm front
to surge northward and should lead to wide-reaching showers and
weak thunderstorms Thursday morning...especailly across western
and central Minnesota. The rain is expected to persist throughout the day
on Thursday and there is also good agreement among guidance to
light up a lot of convection along the cold front in Minnesota Thursday
afternoon and evening. This seems reasonable given the strength of
the fgen and amount of moisture expected to be in place. There is
also between 500-1500j/kg of MUCAPE across the forecast area
throughout the day Thursday.
Friday will likely see a healthy amount of cloud cover...but the
precipitation will have largely shifted east by the time we reach the end
of the work week. After the cold front passes through on
Thursday...the stage will be set for a cool down for the weekend
into early next week. We will likely see temperatures fall back into the
40s and 50s early next week with a nice pocket of cold air that
makes its way down in northwest flow. The thermal profile is warm
enough for all rain on Sunday...but the trend of the wet bulb zero
/wbz/ level with time is interesting with the wbz actually getting
below 1000ft early Tuesday morning for at least a few hours. A wbz
below 1000ft is sometimes a good first guess at whether or not the
boundary layer is waem enough to melt the snowflakes before they
reach the ground. The track for monday's rain maker is still a bit
uncertain in timing and precise placement.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 545 am CDT Wednesday may 6 2015
IFR/LIFR ceilings br over much of the area this morning. This is
ahead of the Iowa warm front which will lift north into southern
Minnesota this afternoon. Some -shra also out ahead of the front and the
main upper trough. Expect ceilings/visibilities to improve to VFR between
17z-18z. More widespread -shra/scattered -stra to move in from the west
again and move to near the Minnesota/WI border through 00z Thursday. This
activity should lift north again through the evening...with more
-shra/-tsra moving in mainly after 06z to the southwest...to near
kmsp through 12z Thursday. Southeast winds expected much of the
day...increasing as pressure gradient increases...with gusts to
20kts into WI and to near 30 kts into SW Minnesota. Expect winds to relax
some this evening.
IFR conditions improving to VFR through 18z. Could see a passing
-shra 14z-18z but the main brunt of activity should hold off until
after 22z. May see some thunder in this time period...depending on
how much sunshine we see. Then this works off to the northeast
this evening before the next round moves in by 12z Thursday. Ceilings may
lower to MVFR as this -shra/thunderstorms and rain arrives. Gutsy southeast winds into the
/Outlook for kmsp/
Thursday afternoon/night...MVFR conds likely with IFR conds possible
in shra/tsra. Winds S 17-25 kts.
Friday...VFR. Winds northwest 7-10 kts.
Sat...VFR. Winds NE 10-15 kts.
Minnesota...dense fog advisory until 9 am CDT this morning for mnz082>085-