692 
fxus63 kapx 240738 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
338 am EDT Thursday Jul 24 2008 


Synopsis...surface high pressure and dry air will result in a 
pleasant day today. Low pressure lifting into Ontario tonight and 
Friday will drag a weak warm front across the region...possibly 
bringing some light rain showers to eastern Upper Michigan. The 
associated cool front will arrive late Friday night...and push 
through by Saturday morning. Scattered showers and possibly a 
thunderstorm or two will impact eastern upper Friday evening...but 
this activity will likely dissipate as it tracks eastward across 
northern lower overnight Friday. Dry air again settles into the 
region for the weekend with partly cloudy skies and seasonable 
temperatures. 




&& 


Discussion...sfc/RUC/satellite/radar and upper air analysis 
showing upper low spinning over the eastern Great Lakes with a 
shortwave diving down across ssm as of 3am. Cloud associated with 
this feature has eroded with time and skies overall were rather 
clear with relatively dry air in place. Winds have decoupled 
across all but the eastern County Warning Area...and temperatures were generally north 
the 50s. Upstream...a decent short wave was lifting northeast into 
Manitoba...associated with surface low pressure. A warm front was 
draped from the low...southward into the Dakotas. Moderate forcing 
and moisture was seen ahead of the short wave. Isolated showers was 
evident across Minnesota with a few thunderstorms on the middle level dry 
slot from southeast Manitoba through far eastern North Dakota. The 
deepest moisture and instability resided from mainly Nebraska to 
western MO. Better thunderstorm activity was ongoing there. 


Today...upper low will lift eastward today while surface ridge of high 
pressure works across the region. Relatively dry air and light 
winds will result in a rather pleasant day again today. Downward 
vertical motions and warming aloft will limit the potential for 
better cumulus development. However cumulus will develop over land 
areas and try and consolidate along lake breezes developing by 
late morning...especially across NE lower. Look for skies to become 
clearer for areas close to the shoreline...as more stable marine 
air penetrates inland through the afternoon. Temperatures will 
climb into the upper 70s/low 80s with 800 mb temperatures at +12 to +13c. 


Tonight...any cumulus will quickly dissipate this evening...but 
middle/upper warm frontal clouds will start to increase from the west 
through the evening. Models are a bit quicker in bringing the 
aforementioned band of somewhat deeper moisture into the region 
overnight tonight. Really do not see much in the way of chance for 
precipitation...as middle level heights actually rise overnight 
(contrary to over Minnesota/Manitoba last night where there was a more 
defined short wave and moderate forcing). However...both NAM/GFS do 
suggest that a weak 25-30kt 800 mb low level jet sneaks into eastern upper with 
800 mb dew points increasing to +10 to +12c. Middle level lapse rates are 
5.5c/km and MUCAPES are none...so thunder is out of the question. 
Could see maybe a few stray light rain showers at most across this 
region and have added them to the forecast. Most folks will more 
likely see a no precipitation night though. 


Friday...warm frontal band of deeper moisture will be lifting 
northeast of the County Warning Area early Saturday morning and SW flow increases 
in the 800 mb-h9 layer to 15-20kts. 800 mb dew points are expected to rise into 
the +10c to +12c range across all of northern Michigan with a broad 
divergent flow developing at 500 mb. Some embedded weakish short wave 
activity will blow into the region...but the marginal low level 
wind speeds may limit the lake breeze development. Best 
convergence would be over NE lower and have kept the 20 percent 
chance for showers/storms at this time. An 84/55 parcel can yield 300-400 
j/kb of MLCAPE/SBCAPE. The best chance for showers and storms 
(only 30 percent chance) will reside across far western areas of 
chip/Mack counties away from onshore flow. This area is where 
modest dry slotting and steeper lapse rates aloft develop by late 
afternoon. 


Friday night...any isolated precipitation across NE lower should 
fall apart will loss of heating...while the best chance again for 
seeing continued showers and storm activity will be across eastern 
upper. Afternoon development will try and sweep eastward across 
this area...but this action will be tied more closely to diurnal 
processes. The actual front will still be upstream...and not set 
to arrive until 06-12z. Diurnal processes will have an influence 
on this precipitation too...but weakish low level jet/-divq ahead of a short wave 
will at least try and help sustain some broken area of rainfall. 
Instability will more than likely be waning as this activity rolls 
through for the overnight hours so the chances for hearing thunder 
will be falling off by this time. Really feel like thunder will 
not occur at all...but cannot justify taking this out at this time. Will 
leave the 30 percent chance in for all areas 06-12z...but actually 
taking probability of precipitation out for a portion of the southeast County Warning Area may be in line. 


Saturday...if anything is able to hold together by Saturday 
morning it would only be across the southeast half of the County Warning Area. GFS 
suggests that front will already have pushed through...but did not 
want to go with a faster solution...as this is typically not the 
norm. Went with a 20 percent chance of showers/storms for the 
morning. Behind the front...surface dew points may not fall off all that 
rapidly right away. However the air mass dries pretty decently 
aloft and through diurnal mixing...dew points lowering into the upper 
40s is not out of the question. Do not see any fire weather 
concerns at this point...as winds will not be much of an issue. 
Low rh's and warm temperatures would be...and makes this Worth 
monitoring. 


Later periods...GFS still more bullish in bringing down deeper low 
level moisture and cooler air with the upper trough...while the 
NAM and European model (ecmwf) are in more agreement in keeping this to our north. 
I have sided with the latter...and have kept any showers out of 
the forecast and kept temperatures warmer than what they would be 
in the GFS is right. Readings in the low to middle 70s look fine. 
Latest European model (ecmwf) does suggest that maybe some of this cooler air and 
moisture could sneak in across the NE County Warning Area Sunday night...but 
current forecast is already steered in this direction. No precipitation 
is forecast into the next work week. Smd 


&& 


Aviation...VFR conditions expected through the taf period. Surface 
high pressure is pretty much in control. The one exception is an 
upper level wave evident on water vapor loop over south central 
Ontario. This feature is moving to the south and it will move across 
northeast lower over the next few hours. However...the lack of 
moisture and loss of daytime heating has dissipated earlier 
convection and do not expect any reformation. Light winds early this 
morning expected to give way to afternoon lake breezes. 


Ajs 




&& 


Apx watches/warnings/advisories... 
Michigan...none. 
Lm...none. 
LH...none. 
Ls...none. 
&& 


$$ 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)