NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260504_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)
=== ===== === ==== ==== === === === ====
Mon 05/04 18Z 8.43 2418  73  58   4 0.00
Mon 05/04 19Z 9.72 2417  70  58   5 0.00
Mon 05/04 20Z 7.60 2420  69  56   5 0.01
Mon 05/04 21Z 5.61 2420  67  58   6 0.00
Mon 05/04 22Z 3.23 2421  66  47   6 0.00
Mon 05/04 23Z 1.25 2422  66  35   6 0.00
Tue 05/05 00Z 1.01 2323  66  27   7 0.00
Tue 05/05 01Z 0.92 2324  65  36   7 0.00
Tue 05/05 02Z 0.92 2327  67  22   7 0.00
Tue 05/05 03Z 0.91 2329  70  14   7 0.00
Tue 05/05 04Z 0.96 2232  72  24   7 0.00
Tue 05/05 05Z 0.92 2234  73  28   7 0.00
Tue 05/05 06Z 0.89 2234  72  39   8 0.00
Tue 05/05 07Z 0.84 2234  71  36   8 0.00
Tue 05/05 08Z 0.83 2233  73  19   7 0.00
Tue 05/05 09Z 0.74 2231  78   9   8 0.00
Tue 05/05 10Z 0.69 2330  83  43   8 0.00
Tue 05/05 11Z 0.72 2332  84  58   8 0.01
Tue 05/05 12Z 0.76 2332  88  73   8 0.01
Tue 05/05 13Z 0.78 2330  87  70   8 0.00
Tue 05/05 14Z 0.79 2328  79  74   9 0.00
Tue 05/05 15Z 0.77 2226  77  74   9 0.00
Tue 05/05 16Z 2.38 2225  78  72   9 0.00
Tue 05/05 17Z 8.58 2225  78  81   9 0.00
Tue 05/05 18Z 7.76 2125  79  86  10 0.00
Tue 05/05 19Z 5.86 2126  79  84  10 0.01
Tue 05/05 20Z 4.98 2128  83  78  11 0.04
Tue 05/05 21Z 4.35 2029  83  84  11 0.07
Tue 05/05 22Z 2.14 2230  88  82  11 0.15
Tue 05/05 23Z 1.22 2233  88  81  10 0.17
Wed 05/06 00Z 1.08 2232  88  81  10 0.10
Wed 05/06 01Z 1.33 2332  86  91   9 0.09
Wed 05/06 02Z 1.24 2430  90  93   8 0.25
Wed 05/06 03Z 0.99 2627  95  97   7 0.17
Wed 05/06 04Z 0.79 2524  93  95   6 0.07
Wed 05/06 05Z 0.82 2621  95  96   5 0.08
Wed 05/06 06Z 0.97 2620  95  95   3 0.08
Wed 05/06 07Z 0.68 2717  97  92   3 0.08
Wed 05/06 08Z 0.44 2614  96  93   3 0.08
Wed 05/06 09Z 0.37 2714  91  89   3 0.04
Wed 05/06 10Z 0.30 2611  84  98   3 0.02
Wed 05/06 11Z 0.29 2511  80  95   3 0.03
Wed 05/06 12Z 0.23 2409  80  96   3 0.02
Wed 05/06 13Z 0.23 2609  81  95   3 0.02
Wed 05/06 14Z 0.16 2407  78  94   3 0.03
Wed 05/06 15Z 0.11 2107  77  89   4 0.03
Wed 05/06 16Z 0.10 2008  81  95   4 0.04
Wed 05/06 17Z 0.09 2007  83  97   4 0.06
Wed 05/06 18Z 0.07 1907  85  94   5 0.07
Wed 05/06 19Z 0.05 1606  88  95   5 0.08
Wed 05/06 20Z 0.07 1506  91  99   5 0.09
Wed 05/06 21Z 0.10 1306  95  99   5 0.11
Wed 05/06 22Z 0.05 1202  96  99   5 0.14
Wed 05/06 23Z 0.07 0702  97  99   5 0.10
Thu 05/07 00Z 0.06 0204  98  99   4 0.10
Thu 05/07 01Z 0.05 3506  98  98   4 0.07
Thu 05/07 02Z 0.05 3509  96  98   3 0.04
Thu 05/07 03Z 0.04 3510  97  99   3 0.07
Thu 05/07 04Z 0.06 3411  96  99   2 0.03
Thu 05/07 05Z 0.14 3313  90  94   2 0.01

Run total areal avg QPF for the greens is: 2.67 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