II. Local Mesoscale Circulation Systems

1
II. Local Mesoscale Circulation Systems

• Upslope Precipitation
• Orographically enhanced Convection
• Downslope Wind Storms

2
View of Western Mountains

• Important flow regimes that maximize upslope
  precipitation for various regions
• Upstream precipitation can deplete an airmass of
  moisture necessary to form upslope precipitation
  at a particular location. Must consider
• Elevation of upstream barriers
• Moisture source region
• Synoptic lifting by airmass

3
(No Transcript)
4
(No Transcript)
5
Diurnal Variation of Upslope Storms

• Seemingly a night time maximum of precipitation
• Apparent reason may be the radiationally cooling
  makes clouds colder , hence
• More efficient
• More likely to cool below dew point

6
(No Transcript)
7
(No Transcript)
8
Rocky Mountain Eastern Slope Upslope Storms

• Upslope usually shallow, ie easterly flow
  confined to below 700 mb
• Gulf Moisture from east necessary
• Surface (850 mb) and 700 mb flow important

9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
Cold Air Damming

• Major upslope storms associated with cold air
  damming
• Artic flow from north moves southward along
  mountain barrier
• Flow wants to turn right (into the barrier) from
  coriolis, forming a trapped Kelvin wave effect,
  ie the cold air warps up against the barrier
• Flow from the east rides up over the cold air,
  producing snow band over the plains

13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
Cold air Damming on East Coast

• East coast storms are famous for the cold air
  damming there
• Similar form to the damming in the Rockies

22
(No Transcript)
23
(No Transcript)