NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260530_1200
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 05/30 12Z 0.55 0323  96  65  -1 0.00
Sat 05/30 13Z 0.54 0322  93  52  -1 0.05
Sat 05/30 14Z 0.43 0319  90  46   0 0.02
Sat 05/30 15Z 0.45 0318  89  43   0 0.01
Sat 05/30 16Z 0.67 0216  89  43   0 0.00
Sat 05/30 17Z 0.98 0114  87  47   0 0.00
Sat 05/30 18Z 1.16 0115  83  46   0 0.00
Sat 05/30 19Z 1.42 0016  80  47   0 0.00
Sat 05/30 20Z 1.91 0116  76  47   0 0.00
Sat 05/30 21Z 1.81 0116  73  50   1 0.00
Sat 05/30 22Z 1.44 0116  70  50   1 0.00
Sat 05/30 23Z 0.85 0116  69  48   1 0.00
Sun 05/31 00Z 0.50 0117  67  41   1 0.00
Sun 05/31 01Z 0.39 0219  65  36   1 0.00
Sun 05/31 02Z 0.32 0119  62  26   2 0.00
Sun 05/31 03Z 0.28 0119  60  18   2 0.00
Sun 05/31 04Z 0.18 0118  63  13   2 0.00
Sun 05/31 05Z 0.14 0016  67  12   2 0.00
Sun 05/31 06Z 0.13 3516  69  13   2 0.00
Sun 05/31 07Z 0.15 3516  72  14   3 0.00
Sun 05/31 08Z 0.19 3415  71  16   3 0.00
Sun 05/31 09Z 0.24 3314  68  18   3 0.00
Sun 05/31 10Z 0.30 3214  68  22   3 0.00
Sun 05/31 11Z 0.44 3115  68  30   4 0.00
Sun 05/31 12Z 0.53 3116  67  31   4 0.00
Sun 05/31 13Z 0.53 3115  67  48   4 0.00
Sun 05/31 14Z 0.62 3115  68  72   4 0.00
Sun 05/31 15Z 1.19 3116  69  83   4 0.00
Sun 05/31 16Z 3.02 3117  75  87   4 0.00
Sun 05/31 17Z 2.31 3115  77  85   4 0.01
Sun 05/31 18Z 0.96 3014  82  89   4 0.01
Sun 05/31 19Z 0.91 2914  85  93   4 0.01
Sun 05/31 20Z 0.93 2915  81  87   4 0.01
Sun 05/31 21Z 1.11 2915  81  79   4 0.01
Sun 05/31 22Z 1.15 2919  83  83   4 0.04
Sun 05/31 23Z 1.08 3021  80  86   4 0.02
Mon 06/01 00Z 0.73 3122  85  86   4 0.03
Mon 06/01 01Z 0.67 3121  82  84   4 0.02
Mon 06/01 02Z 0.65 3220  80  77   4 0.04
Mon 06/01 03Z 0.49 3219  79  67   3 0.06
Mon 06/01 04Z 0.31 3416  79  56   3 0.00
Mon 06/01 05Z 0.17 3413  80  51   3 0.00
Mon 06/01 06Z 0.17 3412  82  62   3 0.00
Mon 06/01 07Z 0.09 3511  83  66   3 0.00
Mon 06/01 08Z 0.09 0109  86  75   2 0.00
Mon 06/01 09Z 0.10 0108  87  73   2 0.00
Mon 06/01 10Z 0.13 0208  87  69   2 0.00
Mon 06/01 11Z 0.19 0408  90  73   1 0.00
Mon 06/01 12Z 0.26 0608  94  76   1 0.00
Mon 06/01 13Z 0.31 0708  95  77   1 0.00
Mon 06/01 14Z 0.35 0809  94  72   1 0.00
Mon 06/01 15Z 0.43 0909  92  64   1 0.00
Mon 06/01 16Z 0.64 0808  91  58   1 0.00
Mon 06/01 17Z 0.99 0706  87  58   1 0.00
Mon 06/01 18Z 1.10 0405  82  55   1 0.00
Mon 06/01 19Z 1.05 0205  79  52   2 0.00
Mon 06/01 20Z 0.89 0106  79  48   3 0.00
Mon 06/01 21Z 0.66 0106  80  51   3 0.00
Mon 06/01 22Z 0.29 0106  79  57   3 0.00
Mon 06/01 23Z 0.08 0007  79  54   3 0.00

Run total areal avg QPF for the greens is: 0.34 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