NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_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 2.69 2812  87  35  14 0.00
Sun 08/09 19Z 2.91 2813  84  40  14 0.00
Sun 08/09 20Z 2.56 2814  82  38  14 0.00
Sun 08/09 21Z 1.80 2814  82  31  14 0.00
Sun 08/09 22Z 1.41 2815  80  30  14 0.00
Sun 08/09 23Z 1.11 2817  83  35  14 0.00
Mon 08/10 00Z 0.92 2917  85  31  14 0.00
Mon 08/10 01Z 0.64 2917  80  36  14 0.00
Mon 08/10 02Z 0.47 2916  73  41  15 0.00
Mon 08/10 03Z 0.39 3015  67  43  16 0.00
Mon 08/10 04Z 0.34 3015  61  46  16 0.00
Mon 08/10 05Z 0.30 3114  58  47  16 0.00
Mon 08/10 06Z 0.26 3213  54  48  16 0.00
Mon 08/10 07Z 0.17 3210  54  46  16 0.00
Mon 08/10 08Z 0.09 3407  55  43  15 0.00
Mon 08/10 09Z 0.08 3403  57  39  15 0.00
Mon 08/10 10Z 0.08 2301  59  35  15 0.00
Mon 08/10 11Z 0.09 2104  63  36  14 0.00
Mon 08/10 12Z 0.09 2006  63  35  14 0.00
Mon 08/10 13Z 0.06 1908  64  31  14 0.00
Mon 08/10 14Z 0.06 1809  64  31  14 0.00
Mon 08/10 15Z 0.11 1910  65  32  14 0.00
Mon 08/10 16Z 0.31 1912  69  35  14 0.00
Mon 08/10 17Z 0.89 2013  73  41  14 0.00
Mon 08/10 18Z 0.85 2116  81  41  14 0.00
Mon 08/10 19Z 0.63 2117  81  46  15 0.00
Mon 08/10 20Z 0.59 2117  78  59  15 0.00
Mon 08/10 21Z 0.55 2117  81  79  16 0.00
Mon 08/10 22Z 0.60 2218  84  73  16 0.01
Mon 08/10 23Z 0.64 2220  90  65  15 0.01
Tue 08/11 00Z 0.75 2223  92  65  15 0.03
Tue 08/11 01Z 0.71 2422  94  75  15 0.24
Tue 08/11 02Z 0.84 2524  94  66  15 0.09
Tue 08/11 03Z 0.86 2724  92  57  15 0.02
Tue 08/11 04Z 0.74 2723  90  55  15 0.01
Tue 08/11 05Z 0.72 2822  93  55  14 0.01
Tue 08/11 06Z 0.70 2822  94  66  14 0.02
Tue 08/11 07Z 0.56 2919  89  65  14 0.02
Tue 08/11 08Z 0.62 2920  90  58  14 0.07
Tue 08/11 09Z 0.66 2820  92  48  13 0.02
Tue 08/11 10Z 0.65 2821  90  45  13 0.02
Tue 08/11 11Z 0.62 2920  90  48  13 0.02
Tue 08/11 12Z 0.58 2919  92  47  13 0.02
Tue 08/11 13Z 0.56 2919  92  40  12 0.02
Tue 08/11 14Z 0.58 2918  93  32  12 0.01
Tue 08/11 15Z 0.56 3017  93  29  12 0.02
Tue 08/11 16Z 0.55 3016  93  21  12 0.01
Tue 08/11 17Z 0.61 3014  93  20  12 0.01
Tue 08/11 18Z 0.67 2914  92  23  12 0.02
Tue 08/11 19Z 0.61 2914  89  24  12 0.01
Tue 08/11 20Z 0.71 2914  87  28  12 0.01
Tue 08/11 21Z 0.60 2915  84  18  12 0.02
Tue 08/11 22Z 0.59 3016  79  18  12 0.01
Tue 08/11 23Z 0.55 3017  77  17  12 0.01
Wed 08/12 00Z 0.53 3017  75  19  12 0.01
Wed 08/12 01Z 0.60 3018  79  25  11 0.01
Wed 08/12 02Z 0.59 3018  83  30  11 0.02
Wed 08/12 03Z 0.56 3018  85  31  10 0.01
Wed 08/12 04Z 0.51 3118  90  26  10 0.01
Wed 08/12 05Z 0.41 3117  89  31  10 0.01

Run total areal avg QPF for the greens is: 0.83 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