Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1115 am CDT sun Apr 26 2015
Updated for 18z aviation discussion below...
Short term...(today and tonight)
issued at 349 am CDT sun Apr 26 2015
A very pleasant day is ahead with a ridge of high pressure holding
steady from western Ontario through Minnesota and Wisconsin. The
sky will be mainly clear today as well as tonight along with a
light northeast to east wind. Highs this afternoon will be similar
those on Saturday with lower to middle 60s forecast...which is
very close to the seasonal normal. The forecast highs today line
up well with mix-down from the NAM at 825mb along with a slight
The real challenge today is how low will dew points drop...
especially across central Minnesota...and the corresponding afternoon
minimum humidity. The low level northeast flow brought dew points
in the single digits and lower teens into northeast Minnesota Saturday
evening. Dew points near 20 degrees are now prevalent across
central Minnesota early this morning. The NAM and rap have a good handle
on the situation and lower dew points to near 15 degrees across
much of central Minnesota this afternoon with around 20 here in the Twin
Cities and west central WI. This results in near 15 percent
minimum humidity this afternoon across much of central Minnesota with 20
percent here in the cities and west central WI. Southern areas of
Minnesota bottom out around 25 percent. Fortunately...the northeast to
east winds are expected to stay at or below 10 miles per hour this afternoon
keeping the fire threat mainly in the limited range with elevated
indicated across west central Minnesota.
Long term...(monday through saturday)
issued at 349 am CDT sun Apr 26 2015
Mild temperatures still look on tap for next week...with two
moisture starved fronts traversing the upper MS River Valley Monday
night/Tuesday and again on Friday.
The trouble maker for model agreement through the extended continues
to be the evolution of the deep closed 500 mb low over New England next
week. Model agreement is not really all that bad until we get to
Thursday...when the GFS starts to become more aggressive with
pushing this low out into the North Atlantic...which allows it to
become considerably more progressive than the Gem/European model (ecmwf) with the
flow across the Continental U.S. To end the work work going into next weekend.
For model preferences...went with a fairly equal blend through
Thursday...leaning more toward the less progressive European model (ecmwf) solution
for Friday into next weekend.
The long term will start off with a picture perfect day on
Monday...with highs in the upper 60s/lower 70s...sunny skies and
light winds. Monday night will feature a shortwave moving into
northern Minnesota...with a weak cold front moving into the area as well.
Precipitation potential still does not look all that great for this
front...with the upper low over Texas keeping any meaningful
moisture well of to our south...with convergence along the boundary
looking weak as well. The European model (ecmwf) continues to be an outlier with the
strength of this wave and the amount of precipitation it generates and
continued the trend of favoring a drier solution for this
front...with just slight chance/low chance probability of precipitation mentioned.
Wednesday and Thursday will feature another Dry Ridge of high
pressure moving through. Only change made to blended forecast here
was to lower dewpoints some both days to account for the mixing
potential. Also blended in some bias corrected numbers into the
highs both days to boost them by a few degrees each day...with
widespread highs in the 70s expected for Wed/Thu.
Next issue in the extended comes Friday with the passage of the next
cold front. Given the differences in the handling of the New England
500 mb low mentioned in the second paragraph...the GFS is quite a bit
faster with bringing the front through than the European model (ecmwf). This spread in
the fronts timing explains the nice smearing of slight chance probability of precipitation
across the area on Friday. This front does have a couple of factors
that can give one a little bit more hope for seeing precipitation with this
boundary as opposed to the one for Monday night. Number one...there
will be no upper low over Texas intercepting moisture streaming
north. Also making the precipitation potential look slightly better is that
the low level convergence looks better on Friday and this front
actually has some 850 mb flow and moisture transport out ahead of it.
Still...the airmass it will be displacing again looks incredibly dry
and with instability lacking...anything we do see looks pretty light
at this point.
As for fire weather concerns next week...humidities each afternoon
look to get down into the 20s/30s. Winds still look light though
through Wednesday...but Thursday and Friday will feature stronger winds
and if the moisture return ends up being rather lacking...we could
have fire weather concerns once again. At this point...Thursday
looks to be the day that has the greatest potential to generate red
flag conditions as our southeast winds will be emanating from a very dry
surface ridge centered over the Great Lakes....while Friday at this
point looks to feature higher dewps with the passing front.
Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1105 am CDT sun Apr 26 2015
VFR/sky clear through the period as a ridge of high pressure moves east
across western Great Lakes. Light NE winds becoming southeast over the
western portion of he area tonight into Monday.
wind is the only problem this period. Should see a more NE
component develop with mix this afternoon...and then light north
into Monday afternoon.
/Outlook for kmsp/
Monday night...VFR. Winds north 5 kts.
Tuesday...VFR. Slight chance of morning -shra. Winds northwest 5-10 kts.
Wednesday...VFR. Wind north 5-10 kts.