NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260518_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)
=== ===== === ==== ==== === === === ====
Mon 05/18 18Z 6.25 2213  68  35  16 0.00
Mon 05/18 19Z 9.06 2216  66  36  16 0.00
Mon 05/18 20Z 5.51 2217  72  55  16 0.01
Mon 05/18 21Z 2.31 2220  76  59  16 0.01
Mon 05/18 22Z 1.01 2119  76  36  16 0.00
Mon 05/18 23Z 0.92 2119  78  40  16 0.00
Tue 05/19 00Z 0.85 2121  81  54  16 0.01
Tue 05/19 01Z 0.95 2223  85  36  16 0.00
Tue 05/19 02Z 0.89 2324  82  19  16 0.00
Tue 05/19 03Z 0.89 2326  77  31  17 0.00
Tue 05/19 04Z 1.16 2330  75  43  17 0.00
Tue 05/19 05Z 1.37 2434  74  42  17 0.00
Tue 05/19 06Z 1.40 2436  74  37  17 0.00
Tue 05/19 07Z 1.38 2436  74  32  17 0.00
Tue 05/19 08Z 1.49 2538  76  29  16 0.00
Tue 05/19 09Z 1.47 2536  78  30  16 0.00
Tue 05/19 10Z 1.36 2633  83  46  15 0.01
Tue 05/19 11Z 1.20 2632  82  38  15 0.01
Tue 05/19 12Z 1.02 2630  81  61  15 0.00
Tue 05/19 13Z 1.09 2629  83  73  14 0.00
Tue 05/19 14Z 0.95 2626  81  69  15 0.00
Tue 05/19 15Z 0.99 2526  81  70  15 0.00
Tue 05/19 16Z 1.07 2524  81  69  15 0.00
Tue 05/19 17Z 1.76 2522  85  67  15 0.00
Tue 05/19 18Z 8.04 2422  85  65  15 0.00
Tue 05/19 19Z 5.79 2523  85  78  15 0.00
Tue 05/19 20Z 6.99 2521  84  65  15 0.00
Tue 05/19 21Z 8.12 2520  84  70  15 0.00
Tue 05/19 22Z 2.88 2522  87  79  15 0.00
Tue 05/19 23Z 1.45 2526  92  88  15 0.03
Wed 05/20 00Z 1.18 2629  87  79  15 0.07
Wed 05/20 01Z 0.96 2629  92  77  15 0.00
Wed 05/20 02Z 0.98 2733  89  75  16 0.00
Wed 05/20 03Z 1.11 2533  88  64  16 0.00
Wed 05/20 04Z 1.18 2434  91  69  16 0.00
Wed 05/20 05Z 1.56 2440  93  78  15 0.07
Wed 05/20 06Z 1.25 2536  90  65  15 0.06
Wed 05/20 07Z 1.08 2634  91  59  15 0.00
Wed 05/20 08Z 0.92 2731  91  55  15 0.01
Wed 05/20 09Z 0.89 2629  91  56  15 0.01
Wed 05/20 10Z 0.90 2629  94  63  14 0.01
Wed 05/20 11Z 0.92 2630  94  65  14 0.01
Wed 05/20 12Z 0.86 2629  94  60  15 0.01
Wed 05/20 13Z 0.89 2726  95  64  14 0.02
Wed 05/20 14Z 0.96 2723  97  65  13 0.03
Wed 05/20 15Z 1.07 2623  97  73  12 0.03
Wed 05/20 16Z 1.13 2723  94  87  12 0.03
Wed 05/20 17Z 1.65 2722  92  92  11 0.03
Wed 05/20 18Z 1.96 2821  85  96  10 0.02
Wed 05/20 19Z 1.77 2921  84  83   9 0.01
Wed 05/20 20Z 3.04 3022  84  52   8 0.00
Wed 05/20 21Z 1.33 3023  84  31   7 0.00
Wed 05/20 22Z 0.57 3124  84  12   6 0.00
Wed 05/20 23Z 0.60 3123  84   5   5 0.00
Thu 05/21 00Z 0.44 3223  78   2   3 0.00
Thu 05/21 01Z 0.35 3225  68   1   3 0.00
Thu 05/21 02Z 0.33 3227  66   2   2 0.00
Thu 05/21 03Z 0.33 3228  68   2   1 0.00
Thu 05/21 04Z 0.33 3229  68   2   0 0.00
Thu 05/21 05Z 0.31 3231  67   1   0 0.00

Run total areal avg QPF for the Central_Greens is: 0.50 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