NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260204_1200
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)
=== ===== === ==== ==== === === === ====
Wed 02/04 12Z 0.68 2813  86  73 -15 0.00
Wed 02/04 13Z 0.63 2916  92  70 -15 0.00
Wed 02/04 14Z 0.60 2917  92  73 -15 0.00
Wed 02/04 15Z 0.47 3016  89  73 -15 0.00
Wed 02/04 16Z 0.42 3015  87  66 -15 0.00
Wed 02/04 17Z 0.47 3016  87  53 -14 0.00
Wed 02/04 18Z 0.50 3015  89  41 -14 0.00
Wed 02/04 19Z 0.50 3015  88  38 -14 0.00
Wed 02/04 20Z 0.59 3015  89  40 -13 0.00
Wed 02/04 21Z 0.65 2916  89  40 -13 0.00
Wed 02/04 22Z 0.64 2917  90  36 -13 0.00
Wed 02/04 23Z 0.52 3018  90  31 -13 0.00
Thu 02/05 00Z 0.38 3118  88  28 -12 0.00
Thu 02/05 01Z 0.35 3117  88  28 -12 0.00
Thu 02/05 02Z 0.35 3017  88  31 -12 0.00
Thu 02/05 03Z 0.35 3016  87  33 -12 0.00
Thu 02/05 04Z 0.35 2915  88  35 -12 0.00
Thu 02/05 05Z 0.38 2916  88  35 -12 0.00
Thu 02/05 06Z 0.40 2917  88  37 -13 0.00
Thu 02/05 07Z 0.42 2917  87  39 -13 0.00
Thu 02/05 08Z 0.44 2918  88  40 -14 0.00
Thu 02/05 09Z 0.49 2919  88  50 -14 0.00
Thu 02/05 10Z 0.50 2919  87  62 -14 0.01
Thu 02/05 11Z 0.53 2920  88  69 -15 0.01
Thu 02/05 12Z 0.54 3020  90  38 -15 0.01
Thu 02/05 13Z 0.51 3019  91   4 -16 0.00
Thu 02/05 14Z 0.43 3018  90   4 -16 0.01
Thu 02/05 15Z 0.37 3117  88   4 -16 0.00
Thu 02/05 16Z 0.35 3115  87   3 -16 0.00
Thu 02/05 17Z 0.35 3114  86   4 -16 0.00
Thu 02/05 18Z 0.32 3113  81   3 -15 0.00
Thu 02/05 19Z 0.29 3114  74   4 -15 0.00
Thu 02/05 20Z 0.26 3114  66   4 -14 0.00
Thu 02/05 21Z 0.22 3114  61   4 -13 0.00
Thu 02/05 22Z 0.18 3214  56   4 -12 0.00
Thu 02/05 23Z 0.15 3214  52   4 -12 0.00
Fri 02/06 00Z 0.13 3212  50   5 -12 0.00
Fri 02/06 01Z 0.11 3211  49   6 -11 0.00
Fri 02/06 02Z 0.09 3209  46   7 -11 0.00
Fri 02/06 03Z 0.07 3206  42   8 -10 0.00
Fri 02/06 04Z 0.06 3105  40  10 -10 0.00
Fri 02/06 05Z 0.06 3105  38  12 -10 0.00
Fri 02/06 06Z 0.06 3004  36  16  -9 0.00
Fri 02/06 07Z 0.06 2503  36  24 -10 0.00
Fri 02/06 08Z 0.06 2304  37  31 -10 0.00
Fri 02/06 09Z 0.07 2206  37  37 -10 0.00
Fri 02/06 10Z 0.08 2206  35  38 -10 0.00
Fri 02/06 11Z 0.09 2206  33  36 -10 0.00
Fri 02/06 12Z 0.10 2306  33  30 -10 0.00
Fri 02/06 13Z 0.09 2206  35  25 -10 0.00
Fri 02/06 14Z 0.07 2107  36  16 -10 0.00
Fri 02/06 15Z 0.06 2008  37  10 -10 0.00
Fri 02/06 16Z 0.07 2009  40   7 -10 0.00
Fri 02/06 17Z 0.08 2009  40  15 -10 0.00
Fri 02/06 18Z 0.08 1909  45  65 -10 0.00
Fri 02/06 19Z 0.10 2009  53  85 -10 0.00
Fri 02/06 20Z 0.13 2009  58  87 -10 0.00
Fri 02/06 21Z 0.12 2010  58  86 -10 0.00
Fri 02/06 22Z 0.10 1912  58  87 -10 0.00
Fri 02/06 23Z 0.10 1913  61  84 -11 0.00

Run total areal avg QPF for the greens is: 0.04 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