401 
fxus65 kslc 201054 
afdslc 


Area forecast discussion 
National Weather Service Salt Lake City Utah 
454 am MDT sun Jul 20 2008 


Synopsis...the high pressure system has moved east over Colorado 
over night and this has allow the monsoonal moisture to surge 
northward across the forecast area. This moisture will deepen and remain 
in place through Tuesday before a drier westerly flow sets in for 
middle week. 




&& 


Discussion...have not been able to detect any distinct features 
within the water vapor imagery overnight to help with forecasting 
timing of when the best chance for convection will be. With a very 
moist air mass moving northward across the region today just about 
any place could see scattered showers and thunderstorms. 
However...the forecast sounding for slc shows a nice inverted-v 
profile up through 600 mb so have leaned toward high based 
thunderstorms across the northern valleys this morning but as the 
precipitable waters  increase to over an inch this afternoon and lifted indices 
lower to below -3 believe that rain will be reaching the ground as 
it overcomes the dry boundary layer. The airmass continues to 
moisten through Tuesday. Tuesday should be the best threat of 
showers and thunderstorms across the north due to the southern 
extent of the dynamics associated with the trough moving across 
Idaho. In the wake of this trough a more westerly flow will spread 
in across northern Utah Wednesday but it looks like a boundary may 
be left behind across central Utah Wednesday for continued chance 
of thunderstorms. Farther south activity may wain slightly Tuesday 
through Thursday but the moisture should remain rather deep there 
through the period. 


In the near term...deep moisture is working its way northward into 
southern Utah today. Have gone with a Flash Flood Watch there 
today. See the hydrology section for details. MOS guidance looked 
suspiciously low for probability of precipitation at Cedar City today considering the 
favorable southeast flow aloft which should track any 
thunderstorms that build over the mountains to their southeast 
right across them. 


The amount of cloud cover will determine not only the temperature 
today for many areas but also the amount of instability making the 
details of the forecast quite difficult to say the least. 


In the long range the ec does not show as much of a southerly flow 
developing at 500 mb as the GFS and therefore tempers the amount 
of moisture moving north. Have leaned toward the ec but because I 
do not see any mechanism totally removing the deep moisture will 
keep a threat of at least isolated showers and thunderstorms over 
many areas through the extended. 






&& 


Hydrology...a Flash Flood Watch has been issued for a large 
portion of southern Utah from noon through this evening. 
Precipitable water values of one inch are forecast along the 
Arizona border this morning and this looks reasonable compared to 
the GOES precipitable water imagery. The NAM forecast these values 
to increase to 1.50 inches by noon at St George. One concern that 
flash flooding may not be widespread is that the flow aloft above 
600 mb may be a little too strong at over 25 kts which could limit 
the total amounts of rain in any one location as the storms will 
be moving. But if training thunderstorms occur then heavy rainfall 
amounts will occur. 


&& 


Aviation...there is a 30 percent chance that the northwesterly lake 
breeze will arrive at the slc terminal between 19-22z this 
afternoon...otherwise expect it to be delayed until after that time. 
Moisture increasing over the area will bring a 20 percent chance of 
thunderstorms to slc this afternoon...especially after 21z. These 
storms could produce occasional wind gusts in excess of 30kt. 


&& 


Fire weather...moisture has already begun to spread into the area 
again this morning. This moisture will remain over the fire district 
through at least Tuesday before a drier airmass gradually works its 
way in during the latter half of the week. Thunderstorm coverage 
will increase for the next few days across most of the fire district 
as a result. Most thunderstorms should produce wetting rainfall over 
southern Utah. However...over parts of northern 
Utah...thunderstorms may initially be dry and produce erratic and 
gusty winds in excess of 40mph. Have issued a Fire Weather Watch for 
dry thunderstorms for northwest Utah for this afternoon. 


&& 


Slc watches/warnings/advisories... 
Utah...Flash Flood Watch from noon Sunday to 10 PM Sunday for utz019- 
utz020-utz021-utz518. 


Fire Weather Watch from noon Sunday to 8 PM Sunday for utz003- 
utz004-utz005. 


Wyoming...none. 


&& 


$$ 


Public...struthwolf 
fire weather...cheng 
aviation...cheng 
hydrology...struthwolf 


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