NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260804_0000
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)
=== ===== === ==== ==== === === === ====
Tue 08/04 00Z 0.73 3125  94  57  10 0.00
Tue 08/04 01Z 0.86 3129  86  23  10 0.00
Tue 08/04 02Z 0.79 3129  79  10  10 0.00
Tue 08/04 03Z 0.78 3128  79   7  11 0.00
Tue 08/04 04Z 0.83 3126  71   4  11 0.00
Tue 08/04 05Z 1.09 3026  68   3  11 0.00
Tue 08/04 06Z 1.06 2926  70   1  11 0.00
Tue 08/04 07Z 1.07 2926  66   4  11 0.00
Tue 08/04 08Z 1.02 2925  65   4  11 0.00
Tue 08/04 09Z 0.98 2924  65   3  11 0.00
Tue 08/04 10Z 1.02 2924  65   2  11 0.00
Tue 08/04 11Z 1.03 2923  61   2  11 0.00
Tue 08/04 12Z 1.02 2924  57   2  11 0.00
Tue 08/04 13Z 0.95 2923  56   2  11 0.00
Tue 08/04 14Z 0.89 2921  54   2  12 0.00
Tue 08/04 15Z 0.81 2919  53   2  12 0.00
Tue 08/04 16Z 0.61 2915  52   2  13 0.00
Tue 08/04 17Z 0.52 2912  54   3  13 0.00
Tue 08/04 18Z 0.48 2809  57   9  14 0.00
Tue 08/04 19Z 0.50 2708  58  16  14 0.00
Tue 08/04 20Z 0.48 2508  60  19  14 0.00
Tue 08/04 21Z 0.38 2408  61  22  15 0.00
Tue 08/04 22Z 0.31 2409  61  27  15 0.00
Tue 08/04 23Z 0.31 2410  58  31  16 0.00
Wed 08/05 00Z 0.31 2410  55  34  16 0.00
Wed 08/05 01Z 0.30 2411  51  34  17 0.00
Wed 08/05 02Z 0.26 2311  48  35  17 0.00
Wed 08/05 03Z 0.25 2311  44  37  18 0.00
Wed 08/05 04Z 0.25 2312  41  37  18 0.00
Wed 08/05 05Z 0.26 2312  40  36  19 0.00
Wed 08/05 06Z 0.28 2413  41  32  18 0.00
Wed 08/05 07Z 0.28 2512  44  26  18 0.00
Wed 08/05 08Z 0.31 2513  49  20  17 0.00
Wed 08/05 09Z 0.31 2612  49  16  17 0.00
Wed 08/05 10Z 0.27 2710  51  10  17 0.00
Wed 08/05 11Z 0.27 2710  55   6  16 0.00
Wed 08/05 12Z 0.21 2808  59   5  16 0.00
Wed 08/05 13Z 0.15 2705  60   5  15 0.00
Wed 08/05 14Z 0.11 2404  60   7  16 0.00
Wed 08/05 15Z 0.14 2404  64   8  15 0.00
Wed 08/05 16Z 0.15 2304  65  10  15 0.00
Wed 08/05 17Z 0.17 2204  63   7  15 0.00
Wed 08/05 18Z 0.31 2205  58   4  15 0.00
Wed 08/05 19Z 0.32 2305  53   2  16 0.00
Wed 08/05 20Z 0.33 2306  50   0  16 0.00
Wed 08/05 21Z 0.27 2307  49   0  16 0.00
Wed 08/05 22Z 0.26 2407  50   0  17 0.00
Wed 08/05 23Z 0.26 2507  58   0  16 0.00
Thu 08/06 00Z 0.27 2508  66   0  16 0.00
Thu 08/06 01Z 0.27 2508  69   0  16 0.00
Thu 08/06 02Z 0.25 2607  67   1  16 0.00
Thu 08/06 03Z 0.23 2607  66   3  17 0.00
Thu 08/06 04Z 0.25 2508  67   9  17 0.00
Thu 08/06 05Z 0.28 2509  70  17  16 0.00
Thu 08/06 06Z 0.33 2511  74  25  16 0.00
Thu 08/06 07Z 0.37 2511  78  41  16 0.00
Thu 08/06 08Z 0.34 2610  77  50  16 0.00
Thu 08/06 09Z 0.32 2610  77  58  16 0.00
Thu 08/06 10Z 0.30 2710  76  59  16 0.00
Thu 08/06 11Z 0.28 2709  76  64  16 0.00

Run total areal avg QPF for the greens is: 0.00 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