NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261010_0000
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 10/10 00Z 0.93 2826  90  87   3 0.00
Sat 10/10 01Z 0.93 2927  95  76   2 0.04
Sat 10/10 02Z 0.87 3026  97  47   1 0.05
Sat 10/10 03Z 0.85 3026  95  23   1 0.03
Sat 10/10 04Z 0.82 3125  94  20   0 0.01
Sat 10/10 05Z 0.73 3124  92   9   0 0.01
Sat 10/10 06Z 0.69 3124  88   9   0 0.00
Sat 10/10 07Z 0.62 3124  81  11   0 0.00
Sat 10/10 08Z 0.56 3124  71  14   0 0.00
Sat 10/10 09Z 0.49 3225  62  14   0 0.00
Sat 10/10 10Z 0.44 3224  57  14   0 0.00
Sat 10/10 11Z 0.38 3224  54  14   0 0.00
Sat 10/10 12Z 0.34 3223  53  12   0 0.00
Sat 10/10 13Z 0.31 3222  52  12   0 0.00
Sat 10/10 14Z 0.28 3221  52  13   0 0.00
Sat 10/10 15Z 0.25 3220  51  16   1 0.00
Sat 10/10 16Z 0.22 3217  49  21   1 0.00
Sat 10/10 17Z 0.19 3314  46  26   1 0.00
Sat 10/10 18Z 0.17 3312  43  30   2 0.00
Sat 10/10 19Z 0.12 3310  39  36   3 0.00
Sat 10/10 20Z 0.10 3308  35  38   4 0.00
Sat 10/10 21Z 0.09 3206  33  36   4 0.00
Sat 10/10 22Z 0.10 3005  29  38   5 0.00
Sat 10/10 23Z 0.08 2904  25  37   6 0.00
Sun 10/11 00Z 0.12 2505  24  39   6 0.00
Sun 10/11 01Z 0.13 2406  22  40   7 0.00
Sun 10/11 02Z 0.13 2307  21  37   8 0.00
Sun 10/11 03Z 0.14 2209  21  33   8 0.00
Sun 10/11 04Z 0.18 2212  20  34   9 0.00
Sun 10/11 05Z 0.21 2213  20  33   9 0.00
Sun 10/11 06Z 0.23 2215  20  33   9 0.00
Sun 10/11 07Z 0.29 2218  20  33   9 0.00
Sun 10/11 08Z 0.32 2219  22  31   9 0.00
Sun 10/11 09Z 0.34 2220  29  29   9 0.00
Sun 10/11 10Z 0.36 2320  32  27  10 0.00
Sun 10/11 11Z 0.35 2319  29  25  10 0.00
Sun 10/11 12Z 0.34 2319  29  24  11 0.00
Sun 10/11 13Z 0.36 2320  31  26  11 0.00
Sun 10/11 14Z 0.39 2321  35  30  10 0.00
Sun 10/11 15Z 0.39 2320  41  31   9 0.00
Sun 10/11 16Z 0.36 2318  48  33   9 0.00
Sun 10/11 17Z 0.32 2317  59  38   9 0.00
Sun 10/11 18Z 0.28 2217  67  48   9 0.00
Sun 10/11 19Z 0.26 2216  77  67   8 0.01
Sun 10/11 20Z 0.22 2114  80  74   8 0.01
Sun 10/11 21Z 0.17 2113  81  78   8 0.01
Sun 10/11 22Z 0.14 2012  83  80   9 0.01
Sun 10/11 23Z 0.13 2012  87  83   8 0.02
Mon 10/12 00Z 0.14 2012  90  86   8 0.04
Mon 10/12 01Z 0.14 2111  92  87   9 0.06
Mon 10/12 02Z 0.15 2209  94  86   9 0.05
Mon 10/12 03Z 0.15 2308  95  85   9 0.04
Mon 10/12 04Z 0.16 2407  95  85   9 0.04
Mon 10/12 05Z 0.15 2606  93  82   9 0.03
Mon 10/12 06Z 0.12 2805  88  79  10 0.01
Mon 10/12 07Z 0.10 3005  88  81  10 0.00
Mon 10/12 08Z 0.13 3107  91  79  10 0.01
Mon 10/12 09Z 0.14 3210  92  70  10 0.00
Mon 10/12 10Z 0.15 3313  92  58   9 0.00
Mon 10/12 11Z 0.15 3315  91  46  10 0.01

Run total areal avg QPF for the greens is: 0.49 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