NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261029_0600
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)
=== ===== === ==== ==== === === === ====
Thu 10/29 06Z 0.40 2516  64  40   8 0.00
Thu 10/29 07Z 0.42 2417  67  29   8 0.00
Thu 10/29 08Z 0.43 2418  71  22   8 0.00
Thu 10/29 09Z 0.45 2418  74  19   8 0.00
Thu 10/29 10Z 0.47 2419  76  18   8 0.00
Thu 10/29 11Z 0.51 2420  78  18   8 0.00
Thu 10/29 12Z 0.57 2522  80  19   7 0.00
Thu 10/29 13Z 0.62 2524  80  23   7 0.00
Thu 10/29 14Z 0.65 2524  80  33   7 0.00
Thu 10/29 15Z 0.68 2424  80  43   7 0.00
Thu 10/29 16Z 0.71 2424  81  55   7 0.00
Thu 10/29 17Z 0.74 2424  81  57   8 0.00
Thu 10/29 18Z 0.75 2423  76  43   8 0.00
Thu 10/29 19Z 0.74 2423  71  47   9 0.00
Thu 10/29 20Z 0.80 2425  75  41   9 0.00
Thu 10/29 21Z 0.82 2427  72  37   9 0.00
Thu 10/29 22Z 0.87 2429  72  46   9 0.00
Thu 10/29 23Z 0.82 2430  73  55  10 0.00
Fri 10/30 00Z 0.83 2432  76  64  10 0.00
Fri 10/30 01Z 0.88 2533  78  86  10 0.00
Fri 10/30 02Z 0.94 2534  82  87   9 0.00
Fri 10/30 03Z 0.98 2536  86  90   9 0.00
Fri 10/30 04Z 1.02 2537  91  93   9 0.02
Fri 10/30 05Z 0.93 2634  96  95   8 0.05
Fri 10/30 06Z 0.81 2729  97  82   8 0.04
Fri 10/30 07Z 0.79 2727  91  61   7 0.02
Fri 10/30 08Z 0.76 2727  82  25   7 0.01
Fri 10/30 09Z 0.69 2826  71  12   7 0.01
Fri 10/30 10Z 0.68 2826  70   7   6 0.00
Fri 10/30 11Z 0.66 2826  72   8   5 0.00
Fri 10/30 12Z 0.64 2826  71   7   4 0.00
Fri 10/30 13Z 0.63 2826  72   4   4 0.01
Fri 10/30 14Z 0.66 2926  74   2   3 0.01
Fri 10/30 15Z 0.70 2926  79   4   1 0.01
Fri 10/30 16Z 0.71 2924  84  10   0 0.00
Fri 10/30 17Z 0.91 2924  90  13   0 0.00
Fri 10/30 18Z 1.19 2923  91  13   0 0.00
Fri 10/30 19Z 1.27 2924  92  15  -1 0.00
Fri 10/30 20Z 1.23 3026  93  17  -1 0.00
Fri 10/30 21Z 1.03 3028  92  15  -2 0.00
Fri 10/30 22Z 0.91 3028  94  17  -2 0.00
Fri 10/30 23Z 0.82 3128  95  20  -2 0.00
Sat 10/31 00Z 0.80 3129  96  22  -3 0.01
Sat 10/31 01Z 0.79 3130  97  25  -3 0.01
Sat 10/31 02Z 0.69 3131  98  29  -3 0.01
Sat 10/31 03Z 0.63 3229  99  33  -3 0.02
Sat 10/31 04Z 0.52 3228  97  31  -4 0.02
Sat 10/31 05Z 0.47 3230  92  29  -5 0.01
Sat 10/31 06Z 0.40 3329  90  19  -5 0.00
Sat 10/31 07Z 0.38 3328  94   9  -6 0.00
Sat 10/31 08Z 0.33 3326  93   8  -6 0.00
Sat 10/31 09Z 0.33 3324  94   8  -6 0.00
Sat 10/31 10Z 0.28 3322  92  13  -6 0.00
Sat 10/31 11Z 0.24 3221  88  22  -5 0.00
Sat 10/31 12Z 0.24 3221  84  17  -5 0.00
Sat 10/31 13Z 0.21 3221  79  19  -4 0.00
Sat 10/31 14Z 0.20 3220  71  22  -4 0.00
Sat 10/31 15Z 0.18 3219  61  25  -3 0.00
Sat 10/31 16Z 0.16 3218  52  21  -2 0.00
Sat 10/31 17Z 0.18 3217  50  21  -2 0.00

Run total areal avg QPF for the Central_Greens is: 0.26 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