NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260227_1200
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 02/27 12Z 0.23 2710  58  67  -8 0.00
Fri 02/27 13Z 0.26 2612  58  68  -7 0.00
Fri 02/27 14Z 0.27 2512  58  75  -7 0.00
Fri 02/27 15Z 0.29 2412  58  81  -7 0.00
Fri 02/27 16Z 0.35 2314  52  85  -7 0.00
Fri 02/27 17Z 0.42 2317  49  85  -6 0.00
Fri 02/27 18Z 0.45 2317  50  80  -6 0.00
Fri 02/27 20Z 0.62 2318  53  83  -6 0.00
Fri 02/27 21Z 0.67 2419  56  82  -6 0.00
Fri 02/27 22Z 0.72 2421  64  76  -6 0.00
Fri 02/27 23Z 0.73 2421  71  72  -5 0.00
Sat 02/28 00Z 0.78 2423  77  67  -5 0.00
Sat 02/28 01Z 0.76 2423  83  58  -5 0.00
Sat 02/28 02Z 0.81 2424  84  55  -4 0.00
Sat 02/28 03Z 0.79 2424  81  59  -4 0.00
Sat 02/28 04Z 0.75 2327  77  53  -3 0.00
Sat 02/28 05Z 0.67 2229  75  44  -2 0.00
Sat 02/28 06Z 0.67 2231  73  31  -2 0.00
Sat 02/28 08Z 0.62 2134  64  27  -1 0.00
Sat 02/28 09Z 0.69 2137  63  28  -1 0.00
Sat 02/28 10Z 0.74 2239  64  28  -1 0.00
Sat 02/28 11Z 0.75 2240  58  28  -1 0.00
Sat 02/28 12Z 0.71 2140  54  51   0 0.00
Sat 02/28 13Z 0.69 2140  57  77   0 0.00
Sat 02/28 14Z 0.73 2241  61  81   0 0.00
Sat 02/28 15Z 0.78 2239  68  90   0 0.00
Sat 02/28 16Z 0.85 2236  83  96   0 0.00
Sat 02/28 17Z 0.87 2234  93  85  -1 0.00
Sat 02/28 18Z 0.88 2333  96  64  -2 0.00
Sat 02/28 19Z 1.00 2430  94  30  -2 0.02
Sat 02/28 20Z 1.12 2528  93  19  -3 0.02
Sat 02/28 21Z 1.00 2626  83  16  -3 0.01
Sat 02/28 22Z 0.92 2724  74  12  -4 0.01
Sat 02/28 23Z 0.63 2822  60  14  -4 0.01
Sun 03/01 00Z 0.51 2923  56  15  -4 0.01
Sun 03/01 01Z 0.39 3022  49  15  -5 0.00
Sun 03/01 02Z 0.29 3120  55  18  -6 0.00
Sun 03/01 03Z 0.19 3117  55  22  -6 0.00
Sun 03/01 04Z 0.14 3114  53  26  -5 0.00
Sun 03/01 05Z 0.14 3114  52  24  -5 0.00
Sun 03/01 06Z 0.10 3111  46  44  -4 0.00
Sun 03/01 07Z 0.08 3108  43  57  -4 0.00
Sun 03/01 08Z 0.08 3007  43  60  -5 0.00
Sun 03/01 09Z 0.08 3007  42  91  -5 0.00
Sun 03/01 10Z 0.09 2906  43  85  -6 0.00
Sun 03/01 11Z 0.11 2907  42  96  -7 0.00
Sun 03/01 12Z 0.13 2706  46  94  -8 0.00
Sun 03/01 13Z 0.10 2605  77  94 -10 0.00
Sun 03/01 14Z 0.08 2404  85  93 -10 0.00
Sun 03/01 15Z 0.07 2104  85  93 -10 0.00
Sun 03/01 16Z 0.05 2102  88  96 -11 0.01
Sun 03/01 17Z 0.03 2900  91  96 -12 0.02
Sun 03/01 18Z 0.04 3203  92  96 -13 0.02
Sun 03/01 19Z 0.06 3305  91  95 -14 0.03
Sun 03/01 20Z 0.11 3207  90  93 -14 0.03
Sun 03/01 21Z 0.13 3210  90  91 -15 0.04
Sun 03/01 22Z 0.16 3214  88  85 -15 0.04
Sun 03/01 23Z 0.20 3218  86  82 -16 0.03

Run total areal avg QPF for the Central_Greens is: 0.30 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