NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260609_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)
=== ===== === ==== ==== === === === ====
Tue 06/09 12Z 0.28 2810  72   2  12 0.00
Tue 06/09 13Z 0.27 2809  73   2  11 0.00
Tue 06/09 14Z 0.26 2807  74   1  11 0.00
Tue 06/09 15Z 0.30 2805  72   1  11 0.00
Tue 06/09 16Z 0.51 2604  69   0  12 0.00
Tue 06/09 17Z 0.87 2505  64   0  12 0.00
Tue 06/09 18Z 1.08 2606  64   0  13 0.00
Tue 06/09 19Z 1.20 2607  74   0  13 0.00
Tue 06/09 20Z 1.05 2508  80   0  13 0.00
Tue 06/09 21Z 0.82 2508  82   1  13 0.00
Tue 06/09 22Z 0.76 2511  84   1  13 0.00
Tue 06/09 23Z 0.61 2513  87   1  13 0.00
Wed 06/10 00Z 0.55 2514  89   1  14 0.00
Wed 06/10 01Z 0.52 2615  89   2  14 0.00
Wed 06/10 02Z 0.49 2715  87   2  14 0.01
Wed 06/10 03Z 0.45 2714  85   3  14 0.01
Wed 06/10 04Z 0.40 2812  84   4  14 0.01
Wed 06/10 05Z 0.41 2813  83   5  14 0.01
Wed 06/10 06Z 0.38 2812  84   6  14 0.01
Wed 06/10 07Z 0.27 2809  79   7  15 0.01
Wed 06/10 08Z 0.25 2808  75  14  15 0.01
Wed 06/10 09Z 0.24 2808  70  22  15 0.01
Wed 06/10 10Z 0.25 2808  72  42  15 0.00
Wed 06/10 11Z 0.26 2708  73  55  15 0.00
Wed 06/10 12Z 0.25 2607  76  67  15 0.00
Wed 06/10 13Z 0.22 2407  77  81  15 0.00
Wed 06/10 14Z 0.22 2407  80  84  15 0.00
Wed 06/10 15Z 0.20 2307  82  86  15 0.01
Wed 06/10 16Z 0.21 2208  88  90  15 0.01
Wed 06/10 17Z 0.17 2108  89  88  15 0.01
Wed 06/10 18Z 0.18 2108  90  92  15 0.01
Wed 06/10 19Z 0.15 2008  89  93  15 0.01
Wed 06/10 20Z 0.13 2007  89  91  15 0.00
Wed 06/10 21Z 0.08 1907  90  93  15 0.01
Wed 06/10 22Z 0.05 1707  91  92  16 0.01
Wed 06/10 23Z 0.06 1708  92  91  16 0.00
Thu 06/11 00Z 0.05 1709  92  94  15 0.00
Thu 06/11 01Z 0.05 1711  92  94  15 0.00
Thu 06/11 02Z 0.08 1812  92  93  15 0.01
Thu 06/11 03Z 0.09 1813  92  90  15 0.05
Thu 06/11 04Z 0.10 1912  92  91  15 0.12
Thu 06/11 05Z 0.12 2011  93  89  15 0.09
Thu 06/11 06Z 0.13 2009  90  87  15 0.08
Thu 06/11 07Z 0.10 2007  89  89  15 0.02
Thu 06/11 08Z 0.07 2005  92  88  15 0.01
Thu 06/11 09Z 0.03 1804  95  89  15 0.01
Thu 06/11 10Z 0.03 1603  95  89  15 0.01
Thu 06/11 11Z 0.06 1403  95  84  15 0.00
Thu 06/11 12Z 0.07 1403  95  79  15 0.00
Thu 06/11 13Z 0.04 1802  96  84  15 0.00
Thu 06/11 14Z 0.04 1602  96  83  15 0.00
Thu 06/11 15Z 0.06 1403  95  79  15 0.00
Thu 06/11 16Z 0.10 1202  94  75  15 0.00
Thu 06/11 17Z 0.09 1503  93  71  15 0.00
Thu 06/11 18Z 0.05 1601  93  72  15 0.00
Thu 06/11 19Z 0.09 1402  92  69  16 0.02
Thu 06/11 20Z 0.15 1302  91  67  16 0.04
Thu 06/11 21Z 0.05 1702  92  70  16 0.03
Thu 06/11 22Z 0.06 1802  93  75  16 0.06
Thu 06/11 23Z 0.05 1902  93  76  16 0.09

Run total areal avg QPF for the greens is: 0.79 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