NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260809_1800
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 08/09 18Z 5.81 2811  84  37  14 0.00
Sun 08/09 21Z 2.95 2813  80  33  14 0.00
Mon 08/10 00Z 1.19 2916  78  34  14 0.00
Mon 08/10 03Z 0.55 3015  68  45  15 0.00
Mon 08/10 06Z 0.29 3212  57  51  15 0.00
Mon 08/10 09Z 0.10 3102  59  41  15 0.00
Mon 08/10 12Z 0.07 1909  63  36  14 0.00
Mon 08/10 15Z 0.24 2013  59  34  15 0.00
Mon 08/10 18Z 1.97 2115  77  52  15 0.00
Mon 08/10 21Z 1.91 2120  77  90  15 0.01
Tue 08/11 00Z 1.79 2424  89  85  14 0.10
Tue 08/11 03Z 0.95 2724  84  74  14 0.06
Tue 08/11 06Z 0.76 2824  92  76  14 0.01
Tue 08/11 09Z 0.73 2822  94  62  13 0.03
Tue 08/11 12Z 0.71 2921  94  46  12 0.03
Tue 08/11 15Z 1.03 2921  95  35  11 0.02
Tue 08/11 18Z 7.56 2918  85  28  11 0.00
Tue 08/11 21Z 6.89 3017  78  26  11 0.00
Wed 08/12 00Z 1.41 3020  81  27  11 0.00
Wed 08/12 03Z 1.20 3119  83  26  10 0.00
Wed 08/12 06Z 0.66 3115  86  31  10 0.00
Wed 08/12 09Z 0.40 3110  84  29  10 0.00
Wed 08/12 12Z 0.33 2907  81  36  10 0.00
Wed 08/12 15Z 0.44 3110  83  32  10 0.00
Wed 08/12 18Z 3.30 2605  78  35  11 0.00
Wed 08/12 21Z 2.49 2604  72  53  12 0.00
Thu 08/13 00Z 0.26 2205  70  70  12 0.00
Thu 08/13 03Z 0.34 2209  70  72  12 0.00
Thu 08/13 06Z 0.60 2314  75  77  12 0.00

Run total areal avg QPF for the greens is: 0.26 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1