Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
412 am CDT Wednesday may 6 2015
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 06z tafs through 06z Wednesday night)
issued at 1030 PM CDT Tuesday may 5 2015
Ceilings and visibilities will continue to degrade tonight as a warm front
lifts north across the area. Scattered rain showers across
central Minnesota/WI will be possible into the early morning hours...but
more widespread showers and thunderstorms are expected to spread
into the western area on Wednesday afternoon...and expand east-
northeast across the area during the evening. IFR ceilings will become
prevalent between 06z and 09z. Visibilities should be primarily 3sm or
greater...with patchy fog possible overnight. Should see
temporary improvement on Wednesday morning as the first wave of
showers lifts north of the area...and then the next batch moves in
from the west during the afternoon...this time with thunder
possible. Southeast winds through the period...with gusts
diminishing tonight then redeveloping on Wednesday morning.
expect IFR ceilings /below 1000 feet/ through the overnight...with
patchy br and showers remaining isolated at best. More widespread
activity expected by 00z Thursday...with isolated thunder possible.
/Outlook for kmsp/
Thursday...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-