NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260718_1800
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)
=== ===== === ==== ==== === === === ====
Sat 07/18 18Z 0.36 2027  91  96  14 0.00
Sat 07/18 19Z 0.41 2028  96  93  14 0.05
Sat 07/18 20Z 0.49 2128  98  93  15 0.03
Sat 07/18 21Z 0.64 2229  98  91  15 0.05
Sat 07/18 22Z 0.71 2327  95  84  15 0.09
Sat 07/18 23Z 0.75 2427  96  84  15 0.07
Sun 07/19 00Z 0.74 2328  97  78  16 0.05
Sun 07/19 01Z 0.86 2428  97  80  15 0.05
Sun 07/19 02Z 0.94 2429  97  75  15 0.15
Sun 07/19 03Z 0.98 2529  97  62  15 0.06
Sun 07/19 04Z 1.03 2729  98  57  14 0.08
Sun 07/19 05Z 0.95 2930  98  62  13 0.08
Sun 07/19 06Z 0.77 3029  97  67  11 0.06
Sun 07/19 07Z 0.62 3128  96  38   9 0.03
Sun 07/19 08Z 0.56 3229  92  21   8 0.02
Sun 07/19 09Z 0.51 3231  92  19   8 0.02
Sun 07/19 10Z 0.47 3231  93  19   8 0.02
Sun 07/19 11Z 0.45 3230  93  17   8 0.01
Sun 07/19 12Z 0.46 3229  92  15   8 0.01
Sun 07/19 13Z 0.45 3227  92  10   7 0.01
Sun 07/19 14Z 0.45 3225  90   6   7 0.01
Sun 07/19 15Z 0.47 3223  87   4   7 0.01
Sun 07/19 16Z 0.63 3220  84   7   7 0.00
Sun 07/19 17Z 4.55 3118  81   9   7 0.00
Sun 07/19 18Z 6.81 3018  76  15   7 0.00
Sun 07/19 19Z 8.62 3018  74  17   7 0.00
Sun 07/19 20Z 10.82 3020  72  15   8 0.00
Sun 07/19 21Z 11.73 3021  68  11   8 0.00
Sun 07/19 22Z 10.71 3021  68  11   8 0.00
Sun 07/19 23Z 5.00 3023  67  11   8 0.00
Mon 07/20 00Z 2.13 3024  64  10   8 0.00
Mon 07/20 01Z 1.99 3126  64   9   8 0.00
Mon 07/20 02Z 1.99 3127  67   8   8 0.00
Mon 07/20 03Z 1.70 3127  71   8   7 0.00
Mon 07/20 04Z 1.28 3125  70   8   7 0.00
Mon 07/20 05Z 1.23 3124  73   8   7 0.00
Mon 07/20 06Z 1.07 3122  75   8   7 0.00
Mon 07/20 07Z 0.70 3220  75   9   7 0.00
Mon 07/20 08Z 0.67 3119  75  13   7 0.00
Mon 07/20 09Z 0.59 3117  74  19   7 0.00
Mon 07/20 10Z 0.53 3116  74  23   8 0.00
Mon 07/20 11Z 0.49 3015  72  31   8 0.00
Mon 07/20 12Z 0.50 3014  74  27   8 0.00
Mon 07/20 13Z 0.56 2914  76  32   8 0.00
Mon 07/20 14Z 0.60 2811  76  38   8 0.00
Mon 07/20 15Z 1.28 2710  76  39   8 0.00
Mon 07/20 16Z 2.49 2709  76  36   8 0.00
Mon 07/20 17Z 2.65 2507  74  31   9 0.00
Mon 07/20 18Z 2.60 2507  74  30   9 0.00
Mon 07/20 19Z 2.40 2408  73  26  10 0.00
Mon 07/20 20Z 2.03 2308  72  30  10 0.00
Mon 07/20 21Z 1.20 2108  70  29  11 0.00
Mon 07/20 22Z 0.58 2109  68  25  11 0.00
Mon 07/20 23Z 0.40 2111  66  22  11 0.00
Tue 07/21 00Z 0.34 2013  63  16  11 0.00
Tue 07/21 01Z 0.34 2016  62  13  11 0.00
Tue 07/21 02Z 0.45 2018  63  15  12 0.00
Tue 07/21 03Z 0.49 2119  61  17  12 0.00
Tue 07/21 04Z 0.51 2121  61  19  12 0.00
Tue 07/21 05Z 0.58 2122  66  21  12 0.00

Run total areal avg QPF for the greens is: 0.96 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