Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261016_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Fri 10/16 18Z 0.68 2427  98  94  11 0.00
Fri 10/16 19Z 0.79 2429  96  84  12 0.02
Fri 10/16 20Z 0.88 2430  97  81  12 0.01
Fri 10/16 21Z 0.92 2527  97  80  11 0.02
Fri 10/16 22Z 1.23 2531  98  96  10 0.16
Fri 10/16 23Z 1.06 2829  97  87   7 0.13
Sat 10/17 00Z 0.80 2927  94  76   5 0.02
Sat 10/17 01Z 0.69 3026  93  68   2 0.01
Sat 10/17 02Z 0.86 3028  93  39   0 0.01
Sat 10/17 03Z 0.86 3128  97  35  -1 0.01
Sat 10/17 04Z 0.64 3127  95  47  -2 0.01
Sat 10/17 05Z 0.52 3227  94  43  -3 0.00
Sat 10/17 06Z 0.53 3228  95  42  -3 0.01
Sat 10/17 07Z 0.49 3229  96  41  -4 0.01
Sat 10/17 08Z 0.43 3329  95  40  -4 0.01
Sat 10/17 09Z 0.40 3329  94  34  -5 0.00
Sat 10/17 10Z 0.40 3328  94  19  -6 0.01
Sat 10/17 11Z 0.36 3327  94   4  -6 0.01
Sat 10/17 12Z 0.37 3327  92   1  -7 0.00
Sat 10/17 13Z 0.39 3327  92   1  -7 0.01
Sat 10/17 14Z 0.33 3326  92   3  -7 0.01
Sat 10/17 15Z 0.30 3224  86   3  -8 0.00
Sat 10/17 16Z 0.29 3223  75   2  -8 0.00
Sat 10/17 17Z 0.26 3323  66   2  -8 0.00
Sat 10/17 18Z 0.25 3321  61   2  -8 0.00
Sat 10/17 19Z 0.47 3320  56   4  -8 0.00
Sat 10/17 20Z 0.94 3321  54   9  -8 0.00
Sat 10/17 21Z 0.61 3220  54  28  -8 0.00
Sat 10/17 22Z 0.54 3221  54  38  -7 0.00
Sat 10/17 23Z 0.50 3222  48  38  -7 0.00
Sun 10/18 00Z 0.38 3222  41  33  -6 0.00
Sun 10/18 01Z 0.31 3222  36  47  -5 0.00
Sun 10/18 02Z 0.25 3220  30  43  -4 0.00
Sun 10/18 03Z 0.23 3219  28  54  -4 0.00
Sun 10/18 04Z 0.23 3217  30  44  -4 0.00
Sun 10/18 05Z 0.25 3117  33  56  -4 0.00
Sun 10/18 06Z 0.30 3117  36  50  -4 0.00
Sun 10/18 07Z 0.39 3018  43  45  -4 0.00
Sun 10/18 08Z 0.45 2918  36  44  -3 0.00
Sun 10/18 09Z 0.44 2919  33  41  -3 0.00
Sun 10/18 10Z 0.39 3020  49  40  -2 0.00
Sun 10/18 11Z 0.36 3020  60  41  -1 0.00
Sun 10/18 12Z 0.32 3119  68  50  -1 0.00
Sun 10/18 13Z 0.29 3117  72  54  -1 0.00
Sun 10/18 14Z 0.27 3015  68  52   0 0.00
Sun 10/18 15Z 0.27 2913  58  47   1 0.00
Sun 10/18 16Z 0.27 2912  49  41   2 0.00
Sun 10/18 17Z 0.29 2813  43  37   2 0.00
Sun 10/18 18Z 0.31 2813  37  34   3 0.00
Sun 10/18 19Z 0.31 2813  35  32   3 0.00
Sun 10/18 20Z 0.29 2712  36  33   4 0.00
Sun 10/18 21Z 0.28 2712  35  33   5 0.00
Sun 10/18 22Z 0.29 2713  32  29   5 0.00
Sun 10/18 23Z 0.29 2714  30  26   6 0.00
Mon 10/19 00Z 0.28 2713  27  27   7 0.00
Mon 10/19 01Z 0.26 2712  22  27   7 0.00
Mon 10/19 02Z 0.24 2611  17  26   7 0.00
Mon 10/19 03Z 0.23 2511  13  27   8 0.00
Mon 10/19 04Z 0.25 2412  13  30   8 0.00
Mon 10/19 05Z 0.27 2413  14  27   8 0.00

Run total areal avg QPF for the Central_Greens is: 0.47 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