Weather

569 
fxus63 kmqt 102026 
afdmqt 


Area forecast discussion 
National Weather Service Marquette Michigan 
425 PM EDT Friday Oct 10 2008 


Synopsis... 
WV imagery and RUC analysis indicated a deep middle/upper level trough 
over the western Continental U.S. And a ridge from the Gulf of Mexico to the 
western Great Lakes leaving SW flow from the SW Continental U.S. Toward Upper 
Michigan. At the surface...a warm front extended NE into southern Minnesota and central WI 
from low pressure over southeast Colorado. Weak shortwaves over northwest Minnesota and western Ontario 
along with 300k isentropic lift north of the warm front supported an 
area of showers from northern Minnesota into Western Lake Superior. Visible loop and surface 
observation showed a middle level cloud deck over most of Upper Michigan with some 
clearing advancing into the south from kimt-kesc. 


&& 


Short term (tonight and saturday)... 


Since the best 300k isentropic lift weakening and lifting north...no 
additional measurable precipitation is expected into west Upper Michigan. Satellite 
trends and RUC 700 mb relative humidity forecast suggests that the back edge of the 
clouds will continue to lift northward this evening with mostly 
clear skies over the area after midnight. Radiational cooling late 
will be balanced by increase in south-southeast boundary layer...keeping winds from 
completely decoupling. So...min readings should fall only to around 
40...near dewpoint values over the area. 


With the warm front lifting north of Upper Michigan and plentiful sunshine 
Saturday...NAM forecast soundings suggest that even with mixing only to 
around 925-900 mb...temperatures should climb into the upper 60s to around 
70. 


Long term (sat night through next fri)... 


Sat night and sun...upper trough over the western states is prognosticated 
to open up some during this period...with an upper low within the 
trough heading NE into southeast Montana by 00z Monday. In addition...models are 
indicating a shortwave over central Kansas at 00z sun to lift into western 
Upper Michigan by 00z. Both features will allow ridging to continue to be 
built up into the County Warning Area Sat night...so outside of some frontogenesis 
rain over Western Lake Superior...the rest of the County Warning Area should be dry. 
Future forecasts will need to monitor western Upper Michigan... 
though...with the new 12z European model (ecmwf) showing the rain also including this 
area. All the other models are dry...and therefore followed the 
majority Route. It appears there will be a better chance for the 
rain over Western Lake Superior to move into western Upper Michigan Sun 
afternoon...thanks to height falls with the shortwave moving in. In 
addition...the shortwave should have a decent amount of moisture to 
work with...given that models show a plume of 1.25-1.5 inch 
precipitable water moving in. Skies Sat night in general look to be 
partly cloudy...and with winds not expected to be all that 
strong...temperatures should drop to the increasing dewpoint values. 
Stayed on the low end of guidance where winds go light...which 
happens to be the crossover temperature. In addition...with the 
increasing moisture...setup looks favorable for some fog where winds 
decouple. Actually decided to go with areas of fog in the south 
central with mav text and graphical guidance showing some decent 
probabilities of low visibilities. Future shifts may need a dense fog 
advisory...especially with southeast upslope flow off Lake Michigan. This southeast wind 
and any morning fog/low stratus makes the temperature forecast 
tricky for sun. Outside of this stratus and before the shortwave 
approaches...there may be a decent period of sunshine. Met guidance 
which shows more sun and mixing to near 850mb (850mb temperatures are near 
13c) brings highs into the middle/upper 70s in the western u.P.. mav 
guidance is about 10 degrees colder. Decided to stay conservative 
given cloud cover concerns...but still raised temperatures a few degrees 
from the previous forecast which results in some low 70s. 


Sun night and Monday...interesting period of the forecast...with some 
uncertainty regarding the details of the upper trough. 12z GFS wants 
to keep the whole western trough more consolidated as it lifts out 
into the High Plains...compared to the NAM/UKMET/Canadian/ECMWF 
which split the trough more into two...though the NAM might be more 
of a compromise. Either way...followed the majority idea which 
continues into the extended...and actually for this period of the 
forecast only matters on the speed of the surface cold front associated 
with the upper trough. For Sun night...included probability of precipitation across much of 
the County Warning Area as the shortwave that was moving into western Upper Michigan continues 
heading east-northeast around the upper ridge...in addition to isentropic lift 
shown on the 310k surface from the NAM/GFS. Probability of precipitation for the central are 
mainly in the evening since after 06z...dnva will take hold in the 
central. The western u.P. May still see some rain after 06z...due to 
precipitation occurring along the cold front which should be approaching northwest 
WI by 12z. Precipitation associated with the cold front will gradually spread 
west to east through the day Monday...but greatest probabilities 
remain in the western County Warning Area where the better height falls are. 
Something to note for precipitation during this time period is Hurricane 
Norbert in the east Pacific. Due to the upper flow around the 
western trough...a lot of the moisture from Norbert will be pulled 
northward through the plains into our County Warning Area. This is noted by models 
showing precipitable water increasing to 1.5 inches or higher... 
which would be 250-300 percent of normal. Therefore...this time period 
may be kind of humid with respect to what middle October should be. The 
increased dewpoints combined with cloud cover will help to keep lows 
well above normal for Sun night...and have raised them about 5 
degrees. Further increases may be necessary depending on how warm 
Sunday is. Raised highs as well on Monday...and in fact the NAM 
shows even warmer conditions as it indicates some breaks in the 
clouds during the day prior to the frontal approach...along with 
850mb temperatures still sitting 12-14c. Did not go as high as the 
NAM...but certainly something to watch. 


Monday night through Friday...extended forecast remains uncertain...thanks 
to the 06z/12z GFS which have a much slower exit of the current 
western upper trough during the beginning of the period compared to 
the 00z/12z ECMWF/Canadian/UKMET...the 00z GFS and the 00z GFS 
ensembles. Since the 06z/12z GFS are a big outlier compared to all 
the other models...will follow the majority. Upper trough at 00z Tuesday 
should be split up into two...one piece heading NE through 
Manitoba/Ontario while another is lingering back over The Four 
Corners. The first piece will continue moving NE to Hudson Bay/northern 
Quebec Monday night into Tuesday...enough to drive the cold front that 
moved into western Upper Michigan at 00z Tuesday across the rest of the County Warning Area. This 
front should stall somewhere near Chicago. Precipitation associated with the 
front expected to end west to east Monday night...with dry weather in 
its wake for Tuesday. Tuesday night and Wednesday look a little more 
interesting...with the European model (ecmwf)/UKMET/Canadian showing the second piece 
of the western trough shearing apart and lifting through Upper 
Michigan. This trough produces an area of deformation precipitation into the 
County Warning Area...and have added some chance probability of precipitation into the forecast for both Tuesday 
night and Wednesday to account for this. Will keep the probability of precipitation low given that 
this is the first model cycle showing the deformation idea...but it 
does sound reasonable. For Wednesday night into Friday...the upper flow 
becomes a lot more progressive...with indications of ridging 
building up in the western states... suggesting downstream troughing 
over the eastern U.S.. airmass for Wednesday night/Thursday does not look as 
cold or moist to allow for lake effect precipitation from any model...so 
removed probability of precipitation for that. Chance probability of precipitation are being added for Thursday night and 
Friday across the County Warning Area...though...with a progressive moving shortwave 
trough crossing the Great Lakes. Airmass is somewhat chilly...with 
850mb temperatures around -2c...but still warm enough to keep precipitation in the 
form of rain. 


Temperature wise...the extended looks relatively mild through 
Tuesday...then starts to cool down after the deformation precipitation moves 
across. Readings should fall to near or possibly slightly below 
normal by Friday. 




&& 


Aviation (for the 18z taf issuance)... 


Although middle clouds ahead of a warm front will move across Upper 
Michigan this afternoon along with some sprinkles early this 
afternoon at kcmx...VFR conditions will predominate this forecast 
period. The low levels are expected to remain dry enough to keep low 
clouds or fog from developing. 


&& 


Marine (for the 4 PM Lake Superior forecast issuance)... 


As a warm front lifts toward Lake Superior...the combination of 
pressure falls over Minnesota and a tightening pressure gradient will boost east-northeast 
winds over Western Lake Superior to 15 to 25 knots this evening. Overnight 
into Saturday...the stronger southeast winds will shift into central and 
Eastern Lake Superior as the warm front lifts to the northeast. 


Southeast 15 to 25 knots winds to start off Sat evening on eastern Superior 
will diminish below 20 knots after midnight Sat night as the pressure 
gradient weakens. However...expect winds to increase again Sun night 
and Monday as a cold front moves into and eventually crossing Lake 
Superior during the day Monday. Ahead of the front...look for southeast winds 
of 15 to 25 knots. Behind the front...winds shift to the west...with up 
to 30 knots winds possible on Western Lake Superior. These west up to 
30 knots winds will spread across all of Lake Superior Monday night...then 
diminish on Tuesday below 20 knots as a ridge of high pressure moves across 
Upper Michigan. For Tuesday night...another cold front will be approaching 
Lake Superior...crossing Lake Superior during the day on Wednesday. SW 
winds of 15 to 25 knots are possible on Western Lake Superior Tuesday 
night...otherwise expect SW to west winds below 20 knots during this 
period. 


Fog will become a concern on Lake Superior Sunday night and 
Monday...due to warm moist air flowing across the cooled Down Lake. 
Rain will also help in the production of fog. Inserted patchy fog 
for now...but dense fog may occur at some point during this period. 


&& 


MQT watches/warnings/advisories... 
Upper Michigan...none. 
Lake Superior...none. 
Lake Michigan...none. 


&& 


$$ 


Synopsis/short term...jlb 
long term...aj 
aviation...jlb 
marine...jlb/aj 

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