Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Marquette Michigan
429 am EDT Monday Jul 14 2014
Short term...(today and tonight)
issued at 428 am EDT Monday Jul 14 2014
Showery and unseasonably cool conditions are expected today as a
potent upper low tracks over the region.
Early this morning...a strong middle/upper low tracking southward into
northern-central Minnesota is beginning to make its turn southeastward.
Meanwhile...a weak trough axis accelerating east-northeast away across Central
Lake Superior and Upper Michigan has kicked off a few light showers across
the east half of the County Warning Area. This activity has been isolated at best
and is expected to move out the County Warning Area over the next few horus.
Today...the overall forecast continues to be on track...with
precipitation coverage expanding across the County Warning Area throughout the day.
Main changes to the forecast were to refine probability of precipitation based off the
latest observation trends and new model guidance. Local 12km WRF and
NCEP hrrr models have handled overnight precipitation evolution fairly well
and are in decent agreement on todays precipitation. Therefore...employed
those in conjunction with the 00z NAM and 00z Gem to determine
precipitation evolution today.
Precipitation is expanding rapidly across The Arrowhead of Minnesota early this
morning and should reach the western County Warning Area by day break.
However...much of this activity is expected to fade as it pulls away
from the main low. Some concerns have appeared with the latest WV
trends of the middle/upper lower. Model guidance is analyzing the low a
touch farther east than subjective analysis would indicate. This
places some doubt on the precipitation coverage across the far northern County Warning Area
this morning and afternoon and the bulk of the forcing digs farther
south into northern WI. Hi-res guidance has picked up on this trend
with subsequent runs...so have cut back on probability of precipitation north of a line from
Ontonagon to Marquette. May need to do this more over the next few
hours depending on the latest observation.
Even with a farther south track...some diurnal heating along with
increased forcing with the northern extent of the middle-level low will
induce numerous showers across the interior County Warning Area. Light winds
initially should allow for showers along the shoreline of Lake
Superior before winds increase from the west-northwest this afternoon and
stabilize the environment. With all factors in place...best precipitation
coverage is expected south of a line from Ironwood to Negaunee to
Manistique after noon.
MUCAPE values reach a meager 200 j/kg in a very narrow profile
across the interior west half this afternoon. While a stray rumble
of thunder will be possible...did not include mention in the
forecast given extremely low coverage. However...with some cape to
work with...showers could be on the heavy side at times.
Tonight...a lull in precipitation is expected this evening across most of
the County Warning Area...though with washed out middle-level forcing around...have
kept isolated showers in the forecast. A deformation/fgen region
along the backside of the middle/upper low will track southeastward
across Western Lake Superior to the northwest County Warning Area by 06z Tuesday. A
3-5 hour window of showers is expected as this band moves
overhead...so have bumped up probability of precipitation to high-end chances late tonight
across the western County Warning Area.
As has been well advertised for many days...temperatures will be quite cool
for mid-July...with highs generally 20 degrees below average. With
the main 800 mb cold-core of 4-5c passing just south of the County Warning Area...temperatures
were a bit tricky. Lowered temperatures a degree or two along the WI border
with clouds and showers will persist through the day. Did increase
temperatures far east as they should see some heating early on. Most
locations should see their maximum temperatures in the 50s around late morning
before showers develop and keep temperatures steady...or possibly
falling...throughout the day.
Long term...(tuesday through sunday)
issued at 347 am EDT Monday Jul 14 2014
NAM shows a closed 500 mb low over lower Michigan 12z Tuesday with the upper
trough axis past the County Warning Area at that point. The trough and low move east
Tuesday and northeast on Wednesday away from the area. Precipitation will be slowly
pulling out on Tuesday and by Wednesday...should be dry. NAM shows the deeper
moisture slowly departing on Tuesday. GFS shows about the same thing
along with the European model (ecmwf) and will use a blend of them for this
Will keep chance probability of precipitation going in the morning for all but the far
western County Warning Area and then slowly diminish probability of precipitation across the east half in
the afternoon. Will go dry then for the forecast Tuesday night through
Wednesday night. Did not make too many changes to the going forecast.
In the extended...GFS and European model (ecmwf) show a 500 mb ridge in the western
U.S. With a broad 500 mb trough across the central and eastern U.S.
12z Thursday. Surface high pressure is in control of the weather then.
Pattern changes little for Friday. On Sat...the upper trough that
remains over the area forms an upper low in it that moves into lower
Michigan 12z Sat. A surface frontal system sits off to the west over the
upper Mississippi River valley for sun then. Temperatures will warm
this forecast period with dry weather prevailing through Sat.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 120 am EDT Monday Jul 14 2014
Showery pattern will be setting in over the next 24hrs as middle/upper
level low drops into the upper Great Lakes. While bulk of the rain showers
activity will occur today...especially in the afternoon...there may be a
few rain showers early this morning at kiwd/kcmx and perhaps ksaw.
Initially...low-levels are dry...so VFR conditions will be the rule
into this morning. During the morning...MVFR ceilings will become more
likely at kiwd/kcmx...and MVFR conditions may then prevail through the
day into the night. Not out of the question that IFR conditions could
develop at kiwd under upslope flow if steadier precipitation develops. With
cooler/more stable air affecting the Keweenaw...there may not be much
rain showers activity there today. At ksaw...it may not be until late
morning/early afternoon that ceilings fall to MVFR. Ceilings at all terminals may
fall to IFR near or just beyond this forecast period.
Marine...(for the 4 am Lake Superior forecast issuance)
issued at 428 am EDT Monday Jul 14 2014
Expect west to northwest winds under 20 knots through Wednesday as broad low
pressure over southeast Ontario exits eastward and high pressure
builds over the northern plains. The strongest winds of around 20
knots are expected late tonight into Tuesday afternoon as the low
pressure strengthens slightly and extends a trough westward across
Lake Huron. High pressure will then build across Lake Superior for
Thursday and Friday...bringing S to SW flow of 10-15 knots.