NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260728_0600
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)
=== ===== === ==== ==== === === === ====
Tue 07/28 06Z 0.21 2011  80  81  15 0.00
Tue 07/28 07Z 0.15 1911  81  74  15 0.00
Tue 07/28 08Z 0.17 2012  83  74  15 0.00
Tue 07/28 09Z 0.09 1913  84  71  15 0.00
Tue 07/28 10Z 0.04 1713  84  72  15 0.00
Tue 07/28 11Z 0.03 1715  84  75  14 0.00
Tue 07/28 12Z 0.05 1717  84  78  14 0.00
Tue 07/28 13Z 0.06 1718  85  80  14 0.00
Tue 07/28 14Z 0.05 1718  87  83  14 0.00
Tue 07/28 15Z 0.13 1718  89  79  15 0.00
Tue 07/28 16Z 0.25 1618  90  77  15 0.00
Tue 07/28 17Z 0.39 1621  91  79  14 0.14
Tue 07/28 18Z 0.53 1622  92  84  14 0.14
Tue 07/28 19Z 0.40 1623  91  91  14 0.16
Tue 07/28 20Z 0.18 1724  91  92  14 0.16
Tue 07/28 21Z 0.14 1724  91  92  15 0.07
Tue 07/28 22Z 0.15 1724  92  90  15 0.01
Tue 07/28 23Z 0.16 1623  94  92  14 0.01
Wed 07/29 00Z 0.15 1725  95  93  14 0.06
Wed 07/29 01Z 0.09 1725  95  94  14 0.02
Wed 07/29 02Z 0.09 1726  91  91  15 0.02
Wed 07/29 03Z 0.10 1726  91  87  15 0.01
Wed 07/29 04Z 0.13 1725  92  84  14 0.01
Wed 07/29 05Z 0.15 1626  93  78  14 0.01
Wed 07/29 06Z 0.19 1627  91  72  14 0.01
Wed 07/29 07Z 0.24 1629  89  70  14 0.01
Wed 07/29 08Z 0.26 1632  87  75  14 0.01
Wed 07/29 09Z 0.29 1631  87  79  14 0.01
Wed 07/29 10Z 0.37 1531  89  78  13 0.02
Wed 07/29 11Z 0.43 1531  88  79  13 0.02
Wed 07/29 12Z 0.51 1431  88  79  13 0.03
Wed 07/29 13Z 0.57 1431  86  79  14 0.02
Wed 07/29 14Z 0.66 1333  84  81  13 0.02
Wed 07/29 15Z 0.79 1336  83  82  13 0.01
Wed 07/29 16Z 0.90 1337  82  86  13 0.01
Wed 07/29 17Z 1.28 1337  84  90  13 0.01
Wed 07/29 18Z 0.93 1337  91  91  13 0.02
Wed 07/29 19Z 0.83 1338  91  91  13 0.06
Wed 07/29 20Z 0.80 1336  91  90  13 0.08
Wed 07/29 21Z 0.75 1335  93  88  13 0.07
Wed 07/29 22Z 0.67 1334  94  85  13 0.07
Wed 07/29 23Z 0.62 1333  94  82  13 0.05
Thu 07/30 00Z 0.61 1233  94  86  13 0.07
Thu 07/30 01Z 0.64 1234  94  90  13 0.06
Thu 07/30 02Z 0.63 1235  96  84  13 0.09
Thu 07/30 03Z 0.57 1334  94  84  13 0.06
Thu 07/30 04Z 0.51 1331  92  84  13 0.02
Thu 07/30 05Z 0.49 1330  92  85  13 0.02
Thu 07/30 06Z 0.48 1328  91  88  13 0.02
Thu 07/30 07Z 0.48 1226  89  92  13 0.01
Thu 07/30 08Z 0.48 1124  88  96  13 0.01
Thu 07/30 09Z 0.47 1121  89  95  13 0.02
Thu 07/30 10Z 0.47 1020  88  96  13 0.02
Thu 07/30 11Z 0.52 0921  89  96  12 0.03
Thu 07/30 12Z 0.53 0822  90  94  12 0.04
Thu 07/30 13Z 0.55 0723  92  95  12 0.07
Thu 07/30 14Z 0.57 0723  91  94  12 0.09
Thu 07/30 15Z 0.57 0823  88  92  12 0.05
Thu 07/30 16Z 0.59 0823  88  90  12 0.03
Thu 07/30 17Z 0.53 0821  89  85  13 0.02

Run total areal avg QPF for the greens is: 2.08 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