Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
640 PM CDT Friday Jul 3 2015
Short term...(this evening through saturday)
issued at 320 PM CDT Friday Jul 3 2015
The short term concerns remain extent of any convection along the
weak surface boundary tonight and smoke/fog encroachment tonight
Latest hires models/cams continue indicate some small chance of
isolated/widely scattered thunderstorms and rain over eastern portion of the County Warning Area into
the evening as boundary sags in. Will continue this threat through
about 03z from extreme east central Minnesota into west central Wisconsin.
Latest Storm Prediction Center mesoanalysis quite unstable along the boundary...now
moving into extreme northeast portion of the County Warning Area. Expect this to
gradually end after sunset.
Smoke is gradually filtering into the northwest County Warning Area...and is
expected to continue to do so. Visibility reduction has been minor thus
far...afternoon mixing is providing some improvement over northwest
Minnesota. Still...air quality model diagnostics show smoke area dropping
over central Minnesota during the night. Will mention areas/patchy smoke
over the northwest County Warning Area. Then some fog potential to the far
east...although sref probabilities are marginal. Still...with some
isolated shower activity into the evening...and light winds and
boundary in the area...we could see some fog form into west central
Next problem is extent of any redeveloping rain showers/thunderstorms and rain into eastern
areas Saturday afternoon/evening. Some models still try to develop
some isolated activity over this region Monday/afternoon. Still
will have weak boundary in the vicinity and MUCAPES are forecast to
increase to 1500-2000 j/kg in the afternoon along and north of weak
warm front. Will hold onto slight chance probability of precipitation for isolated threat
in the afternoon across the far east for now.
Long term...(saturday night through friday)
issued at 320 PM CDT Friday Jul 3 2015
The long term portion of the forecast will feature the passage of
a cold front early on with cooler temperatures resulting as a
broad area of surface high pressure builds across the region.
Still expect the evening of the fourth to be dry...although high
clouds will be on the increase ahead of the next approaching
trough and there will still be some residual Canadian wildfire
smoke around. 12z models were fairly agreeable regarding timing
of the next front to come...which should be entering far west central
Minnesota at 00z Monday. Will likely see storms sneak into the far
western part of the forecast area on Sunday afternoon...with showers
and thunderstorms expanding eastward and becoming widespread
between 00z and 12z Monday. Given the orientation of the trough
will be positively tilted in nature...deep layer shear ahead of
the front will not be impressive. However...steep middle level lapse
rates and prognosticated mixed layer convective available potential energy near 2000 j/kg will yield the
potential for a few severe storms. Middle level height falls are
expected as the attendant shortwave pivots from the Dakotas
toward west central Minnesota during the afternoon as well...which will
aid in the atmospheric destabilization process. After the evening
threat for severe storms over west central Minnesota...the primary
concern may transition to a heavy rainfall threat...as
precipitable water values forecast to soar above 2 inches.
Widespread rainfall amounts in the 1-2 inch range appear quite
By 18z Monday...today/S 12z run of model solutions generally
positioned the front along or just west of Interstate 35. Most of
the showers and thunderstorms should be located east of there
Monday afternoon...with precipitation entirely out of the area by late
Behind the front...cooler...less humid...and dry weather sets in
for Tuesday. Highs in the 70s and lows in the 50s should generally
prevail. While there are no major systems prognosticated...semi-zonal
flow will keep the opportunity for weak shortwaves to pass over.
The first is prognosticated for Wednesday into Thursday. Have included 20
probability of precipitation at this point due to low confidence in timing and overall
existence of said feature.
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 630 PM CDT Friday Jul 3 2015
The main issue tonight through tomorrow morning will be chances
for haze/smoke over our area from the wildfires in Canada.
Visibilities have dropped into the IFR range at axn already...and
should remain MVFR/IFR at that terminal through the rest of the
night as an inversion develops after sunset. Smoke/haze has also
moved over the St. Cloud terminal...and it looks like after sunset
some MVFR conditions could develop there as well. The smoke has
been confined to the upper levels at the remainder of our
terminals...but MVFR visibilities cannot be ruled out as the
thicker smoke continues to push southeastward. Models show patchy
fog reducing visibilities at eau and rnh by the early morning as
well...but smoke in the upper levels could reduce radiational
cooling overnight and therefore confidence in fog development is
low at this time.
Kmsp...the smoke currently pushing southeastward over central and
western Minnesota could impact msp after sunset...and with the inversion
developing at low levels overnight there is a possibility that
visibility will be reduced. Have kept visibility at 6sm or higher
in the taf for the rest of the night...but the potential exists
for MVFR...especially after 06z. Visibility should improve shortly
after sunrise...with VFR expected through the remainder of the
period. Winds will remain light throughout the period.
/Outlook for kmsp/
Sat night...VFR. Winds S 5-10 kts.
Sun...VFR. Thunderstorms and rain with MVFR/IFR likely late. Winds S 10-15 kts.
Monday...MVFR/IFR with thunderstorms and rain early then VFR. Winds northwest 10 kts.