NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260506_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 05/06 12Z 0.13 2012  95  96   6 0.00
Wed 05/06 13Z 0.24 2016  97  96   6 0.05
Wed 05/06 14Z 0.25 2017  98  96   6 0.07
Wed 05/06 15Z 0.25 2017  98  98   7 0.08
Wed 05/06 16Z 0.21 2016  99  99   7 0.12
Wed 05/06 17Z 0.22 2015  99  99   6 0.16
Wed 05/06 18Z 0.13 2011  99  99   7 0.16
Wed 05/06 19Z 0.11 1911  98  99   8 0.18
Wed 05/06 20Z 0.24 2412  99  99   7 0.16
Wed 05/06 21Z 0.28 2713  98  97   6 0.07
Wed 05/06 22Z 0.25 3014  97  97   5 0.03
Wed 05/06 23Z 0.22 3113  95  96   4 0.01
Thu 05/07 00Z 0.24 3113  92  97   3 0.00
Thu 05/07 01Z 0.26 3013  88  93   3 0.00
Thu 05/07 02Z 0.29 3014  82  84   2 0.00
Thu 05/07 03Z 0.29 3014  81  77   2 0.00
Thu 05/07 04Z 0.29 3013  81  49   2 0.00
Thu 05/07 05Z 0.32 3013  82  54   1 0.00
Thu 05/07 06Z 0.40 3014  86  44   0 0.00
Thu 05/07 07Z 0.41 3014  86  47   0 0.00
Thu 05/07 08Z 0.49 2916  89  52   0 0.00
Thu 05/07 09Z 0.47 2915  90  46   0 0.00
Thu 05/07 10Z 0.50 2815  92  42   0 0.00
Thu 05/07 11Z 0.52 2815  93  47  -1 0.00
Thu 05/07 12Z 0.57 2816  89  36  -1 0.01
Thu 05/07 13Z 0.46 2812  75  28  -1 0.00
Thu 05/07 14Z 0.65 2711  74  21  -2 0.00
Thu 05/07 15Z 2.35 2711  76  21  -2 0.00
Thu 05/07 16Z 6.64 2812  78  23  -2 0.00
Thu 05/07 17Z 7.77 2812  76  25  -1 0.00
Thu 05/07 18Z 7.93 2812  74  26  -1 0.00
Thu 05/07 19Z 8.64 2813  72  26   0 0.00
Thu 05/07 20Z 8.53 2813  69  27   0 0.00
Thu 05/07 21Z 9.10 2814  66  30   0 0.00
Thu 05/07 22Z 7.78 2914  63  30   0 0.00
Thu 05/07 23Z 5.49 2916  63  34   0 0.00
Fri 05/08 00Z 2.64 2918  64  32  -1 0.00
Fri 05/08 01Z 1.96 3020  71  24  -1 0.00
Fri 05/08 02Z 1.70 3021  72  26  -2 0.00
Fri 05/08 03Z 1.50 3021  75  29  -2 0.00
Fri 05/08 04Z 1.19 2921  76  31  -2 0.00
Fri 05/08 05Z 0.98 3021  77  40  -2 0.00
Fri 05/08 06Z 0.88 3020  73  49  -2 0.00
Fri 05/08 07Z 0.74 3018  73  60  -2 0.00
Fri 05/08 08Z 0.72 3018  74  60  -3 0.00
Fri 05/08 09Z 0.71 3018  74  58  -3 0.00
Fri 05/08 10Z 0.69 2917  76  52  -3 0.00
Fri 05/08 11Z 0.66 2916  77  52  -3 0.00
Fri 05/08 12Z 0.68 2916  79  54  -3 0.00
Fri 05/08 13Z 1.86 2915  80  54  -3 0.00
Fri 05/08 14Z 6.24 2913  80  58  -3 0.00
Fri 05/08 15Z 8.30 2812  76  65  -3 0.00
Fri 05/08 16Z 8.00 2713  77  73  -2 0.00
Fri 05/08 17Z 8.72 2713  73  73  -2 0.00
Fri 05/08 18Z 7.38 2714  74  68  -2 0.00
Fri 05/08 19Z 9.37 2814  70  63  -2 0.00
Fri 05/08 20Z 7.98 2814  71  51  -2 0.00
Fri 05/08 21Z 7.98 2813  67  39  -1 0.00
Fri 05/08 22Z 7.51 2813  67  38  -1 0.00
Fri 05/08 23Z 4.55 2713  66  36  -1 0.00

Run total areal avg QPF for the greens is: 1.10 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