NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260808_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)
=== ===== === ==== ==== === === === ====
Sat 08/08 18Z 0.61 2306  93  68  16 0.00
Sat 08/08 19Z 0.47 2309  92  62  16 0.02
Sat 08/08 20Z 0.41 2311  90  66  16 0.02
Sat 08/08 21Z 0.49 2411  89  63  16 0.04
Sat 08/08 22Z 0.51 2512  91  72  16 0.10
Sat 08/08 23Z 0.47 2513  87  70  16 0.14
Sun 08/09 00Z 0.45 2613  85  73  16 0.09
Sun 08/09 01Z 0.46 2814  85  66  16 0.03
Sun 08/09 02Z 0.38 2811  86  53  16 0.00
Sun 08/09 03Z 0.43 2712  89  47  15 0.00
Sun 08/09 04Z 0.49 2614  92  40  15 0.00
Sun 08/09 05Z 0.48 2615  89  38  16 0.00
Sun 08/09 06Z 0.58 2618  90  44  16 0.00
Sun 08/09 07Z 0.59 2519  89  60  16 0.00
Sun 08/09 08Z 0.70 2522  90  57  15 0.00
Sun 08/09 09Z 0.70 2622  93  54  15 0.00
Sun 08/09 10Z 0.64 2721  91  55  15 0.01
Sun 08/09 11Z 0.57 2819  90  48  15 0.01
Sun 08/09 12Z 0.57 2819  92  40  15 0.01
Sun 08/09 13Z 0.56 2818  92  34  14 0.01
Sun 08/09 14Z 0.51 2817  87  19  15 0.01
Sun 08/09 15Z 0.47 2816  78  17  15 0.01
Sun 08/09 16Z 0.56 2816  82  14  15 0.01
Sun 08/09 17Z 0.76 2816  89  16  14 0.01
Sun 08/09 18Z 0.64 2817  89  24  14 0.01
Sun 08/09 19Z 0.68 2817  88  33  14 0.01
Sun 08/09 20Z 0.71 2917  86  30  14 0.01
Sun 08/09 21Z 0.56 2916  80  25  15 0.01
Sun 08/09 22Z 0.48 2915  74  29  15 0.00
Sun 08/09 23Z 0.51 2916  70  26  15 0.00
Mon 08/10 00Z 0.57 2918  74  29  15 0.00
Mon 08/10 01Z 0.55 2918  72  28  15 0.00
Mon 08/10 02Z 0.48 2917  75  31  15 0.00
Mon 08/10 03Z 0.41 2916  70  33  16 0.00
Mon 08/10 04Z 0.40 2916  67  34  16 0.00
Mon 08/10 05Z 0.38 2915  61  37  16 0.00
Mon 08/10 06Z 0.37 2915  56  38  16 0.00
Mon 08/10 07Z 0.33 3013  55  36  16 0.00
Mon 08/10 08Z 0.38 3013  58  36  15 0.00
Mon 08/10 09Z 0.34 3012  60  36  14 0.00
Mon 08/10 10Z 0.20 3208  61  37  14 0.00
Mon 08/10 11Z 0.09 3103  60  35  14 0.00
Mon 08/10 12Z 0.09 2303  59  33  15 0.00
Mon 08/10 13Z 0.12 2106  59  38  15 0.00
Mon 08/10 14Z 0.17 2108  58  58  15 0.00
Mon 08/10 15Z 0.20 2209  58  71  14 0.00
Mon 08/10 16Z 0.28 2209  59  89  14 0.00
Mon 08/10 17Z 0.34 2210  55  85  14 0.00
Mon 08/10 18Z 0.49 2211  55  74  15 0.00
Mon 08/10 19Z 0.60 2311  59  70  15 0.00
Mon 08/10 20Z 0.37 2309  60  76  15 0.00
Mon 08/10 21Z 0.40 2310  67  75  15 0.00
Mon 08/10 22Z 0.39 2211  77  82  14 0.01
Mon 08/10 23Z 0.26 2012  83  85  15 0.02
Tue 08/11 00Z 0.35 2115  89  91  14 0.03
Tue 08/11 01Z 0.49 2119  92  87  14 0.06
Tue 08/11 02Z 0.61 2321  94  72  15 0.08
Tue 08/11 03Z 0.64 2519  97  70  14 0.01
Tue 08/11 04Z 0.72 2621  96  68  14 0.01
Tue 08/11 05Z 0.66 2619  95  37  14 0.01

Run total areal avg QPF for the greens is: 0.79 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