Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Marquette Michigan
452 am EDT Wednesday Jul 30 2014

Short term...(today and tonight)
issued at 451 am EDT Wednesday Jul 30 2014

The short wave and cold front that led to the scattered/isolated
showers over portions of Upper Michigan yesterday has slid south
of the County Warning Area and is dissipating over central Wisconsin. Dry air
and subsidence behind these features has produced mostly clear
skies over Upper Michigan. 3am temperatures have fallen into the middle
40s to lower 50 as a result of the radiational cooling from the
clear skies...which has also created patchy-areas of ground fog. At
this point...the thickest fog and low stratus is located over the
east (visibilities down to 3/4mi at kery and 1/2mi at kisq) where
fog over Eastern Lake Superior has moved on shore. Over the far
west (gogebic/Ontonagon counties) fog has developed over areas
that experienced showers yesterday. This fog should quickly
dissipate shortly after daybreak with the mostly sunny start to the

Focus today will be on the first shortwave to affect the
area in the short term period (currently moving south through far
northern ontario). Ahead of the wave...a 65-75kt 200-250mb jet
streak will rotate through...but it is slightly separated from the
shortwave. There are some indications that shortwave will weaken as
it moves through the area...but there should still be enough
support of shower development over portions of the area. Seeing
decent middle level moisture ahead of the shortwave (very moist profile
on the 00z cwzc)...although much of this moisture will rotate
around the upper low over James Bay and slide to the east of the
area. But as the shortwave slides southeast across the eastern half
of the County Warning Area will bring a pocket of better moisture across
the County Warning Area during the afternoon. Thus...think the combination of the
increasing moisture and diurnal heating should produce scattered to
broken cloud cover during the afternoon. Shower development is a
little more uncertain...largely due to the later arrival of the
best moisture and shortwave during the late afternoon and into the
early evening. Tried to follow high resolution models for the probability of precipitation
for today...with the idea of a some isolated shower development
over the central and where lake...near Lake Michigan and north
central near Lake Superior. It seems the high resolution models
have started to trend away from the more widespread showers that
were indicated over the last day...largely due to the drier low
level air and later shortwave arrival. Thus...current forecast for
slight/chance probability of precipitation in the previously mentioned areas may be
overdone and might have to be trimmed back. In addition...expect
some development just to the north of Lake Superior as the shortwave
moves through there during peak heating...which should slide
southeast across Lake Superior and into the area late this afternoon
and into the evening hours. This will probably be the better
opportunity for some isolated showers over the northwest half of
the County Warning Area today/tonight. As for thunder...think opportunity is
becoming more limited...especially since the 06z run of the NAM has
finally locked into the other models on lower dewpoints today
(which has caused it to cut way back on diurnal precip). This
lowered MLCAPES to be more in line with everything else and
generally 50-200 j/kg. Will cap thunder mention to slight
chances...but think the best chances will be tied to the shortwave.
Highs today will continue the below normal trend and rise into the
upper 60s to middle 70s.

Tonight...second shortwave (currently over eastern Hudson bay) will
sweep southeast over the northeast half/third of the County Warning Area. Expect
any lingering showers with the shortwave to diminish as they
slide southeast across the County Warning Area. Otherwise...with the better moisture
over the northeast third...think areas over Eastern Lake Superior
would have the best shot of an isolated shower. They could end up
sneaking into eastern portions of the County Warning have held onto
slight chances there through much of the night. Clearing behind the
shortwave over the west could lead to some fog development and have
mentioned patchy fog...although it may be dependent on where
showers occur. The central and east may also see some patchy
fog...but it will largely depend on the amount of cloud cover.

Long term...(thursday through tuesday)
issued at 414 am EDT Wednesday Jul 30 2014

Upper low that has impacted the weather pattern over the Great Lakes
this week persists through late this week. Until the low loses its
influence...forecast will continue to feature chances of mainly
afternoon and evening showers and possible thunderstorms Thursday
and Friday.

On Thursday...with the low still in the vicinity of James Bay...NAM/GFS
/Gem-New Hampshire and European model (ecmwf) all indicate batch of higher 700 mb-500 mb relative humidity dropping
across the upper Great Lakes. Surface front in the vicinity of Upper Michigan
should lead to low-level convergence. Timing of the front will be
important though as if the frontal passage is quicker north-northwest winds will result in
more stable flow across much of County Warning Area by peak heating of Thursday afternoon.
Gem-regional and NAM quite on board with that idea indicating little
if any rain showers/thunderstorms and rain on Thursday. Will show the higher probability of precipitation...only lower
chances...over the far scntrl during the afternoon where greater convergence
would be from the larger scale front and Lake Michigan lake breeze.
Overall though...seems that models are trending away from much in way
of rain showers/thunderstorms and rain on Thursday as stabilizing flow off Lake Superior is
dominant factor.

High pressure begins to slide across later Thursday night. Lowered
temperatures into the middle 40s for cool spots for the interior. Some fog is
possible late Thursday night into daybreak on Friday...especially
for areas that see rain on Thursday afternoon. On into the daytime on
Friday...gradient northwest/north flow is not as strong as Thursday with the
high settling overhead. Result will be More Lake breezes and better
shot at instability to build up over inland areas during peak
heating of the day as maximum temperatures reach middle 70s most areas. If there
is a decent shortwave or pocket of enhanced moisture/lift rotating
around the departing upper the latest European model (ecmwf) indicates...then
would expect much greater coverage to the showers and better shot at
thunderstorms and rain as well given the warmer surface temperatures. Based on where highest
MLCAPES are forecast and with 700 mb winds from chance of thunderstorms and rain
would be along WI border over Iron/Dickinson/Menominee counties.

Heights rise a bit by Saturday as the low begins to fill and surface
high slides across and this is looking like a dry day for the most
part. More troughing aloft expected Sunday into early next week. A
couple surface fronts cross the area as well which should increase chances
for showers and thunderstorms. Consensus probability of precipitation showing Middle Range
chance probability of precipitation seemed good...maximizing on Sunday afternoon through Sunday
evening...then again on Monday as main frontal passage occurs. GFS
and Gem-New Hampshire point to stronger storms more likely on Monday as deep
layer shear ramps up over 30 kts and MLCAPES increase to 1000j/kg. On
the flip side...European model (ecmwf) would suggest Sunday afternoon for stronger storms.
Either way...neither day looks like a sure bet for strong storms...which
is basically a persistence forecast for this Summer thus far in terms
of severe weather across Upper Michigan.

High pressure builds back over the upper Great Lakes in wake of the
trough for Tuesday and Wednesday resulting in dry weather by that
time. Generally seems that overall pattern of below normal temperatures
will persist into next week...though trend will be toward only
slightly below normal temperatures. Drier than normal pattern is forecast
to perist right on through middle August per medium range models and
latest CPC forecasts.

Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 137 am EDT Wednesday Jul 30 2014

Expect fog to impact all the taf sites early this morning with middle level
drying over the low level moisture...with conditions falling as low as LIFR/
vlifr mainly at the more sheltered saw/iwd sites. This fog will burn
off after sunrise. More rain showers may then impact cmx and especially saw in
the afternoon as another disturbance crosses eastern Upper Michigan in the presence
of daytime heating. Although any heavier rain showers that moves over these
sites could result in MVFR or even IFR conditions for a brief
time...VFR weather will predominate. Any rain showers will diminish in the evening
following the departure of the disturance and loss of daytime

Marine...(for the 4 am Lake Superior forecast issuance)
issued at 451 am EDT Wednesday Jul 30 2014

With a weak pressure gradient typical of Summer dominating this
forecast period...expect winds under 20 kts through Sunday.

There is the potential for some patchy/areas of fog over the next
several days over portions of Lake Superior...but Don/T expect any
widespread dense fog.

MQT watches/warnings/advisories...
Upper Michigan...
Lake Superior...
Lake Michigan...


Short term...srf
long term...jla

National Weather Service Glossary of Abbreviations