NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260727_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)
=== ===== === ==== ==== === === === ====
Mon 07/27 12Z 0.09 2402  80  74  13 0.00
Mon 07/27 13Z 0.08 2402  80  71  13 0.00
Mon 07/27 14Z 0.10 2301  82  70  13 0.00
Mon 07/27 15Z 0.17 2302  85  72  13 0.00
Mon 07/27 16Z 0.33 2302  84  74  14 0.04
Mon 07/27 17Z 1.09 2605  83  73  14 0.08
Mon 07/27 18Z 1.12 2604  81  69  14 0.04
Mon 07/27 19Z 1.03 2503  81  66  14 0.02
Mon 07/27 20Z 0.80 2404  82  63  14 0.03
Mon 07/27 21Z 0.33 2203  84  60  14 0.04
Mon 07/27 22Z 0.10 2003  85  60  14 0.04
Mon 07/27 23Z 0.04 1704  85  66  14 0.04
Tue 07/28 00Z 0.23 2107  84  75  14 0.08
Tue 07/28 01Z 0.18 2009  79  73  14 0.05
Tue 07/28 02Z 0.15 2010  80  70  14 0.00
Tue 07/28 03Z 0.28 2111  82  69  14 0.00
Tue 07/28 04Z 0.25 2111  82  61  14 0.00
Tue 07/28 05Z 0.34 2113  84  61  14 0.00
Tue 07/28 06Z 0.36 2213  85  58  14 0.00
Tue 07/28 07Z 0.24 2111  86  51  14 0.00
Tue 07/28 08Z 0.16 2010  87  53  14 0.00
Tue 07/28 09Z 0.09 1910  86  60  14 0.00
Tue 07/28 10Z 0.08 1911  87  66  14 0.00
Tue 07/28 11Z 0.07 1813  89  66  14 0.00
Tue 07/28 12Z 0.04 1814  90  66  14 0.00
Tue 07/28 13Z 0.03 1815  92  72  14 0.00
Tue 07/28 14Z 0.08 1716  93  70  14 0.00
Tue 07/28 15Z 0.06 1716  94  69  14 0.00
Tue 07/28 16Z 0.09 1716  96  72  14 0.01
Tue 07/28 17Z 0.19 1616  95  69  14 0.01
Tue 07/28 18Z 0.23 1617  93  75  14 0.02
Tue 07/28 19Z 0.31 1516  94  72  14 0.03
Tue 07/28 20Z 0.29 1619  95  72  14 0.03
Tue 07/28 21Z 0.24 1718  96  78  14 0.07
Tue 07/28 22Z 0.14 1718  93  75  14 0.14
Tue 07/28 23Z 0.14 1717  93  83  14 0.04
Wed 07/29 00Z 0.11 1718  95  89  13 0.15
Wed 07/29 01Z 0.10 1717  95  90  13 0.22
Wed 07/29 02Z 0.08 1717  96  91  13 0.17
Wed 07/29 03Z 0.18 1621  97  95  13 0.17
Wed 07/29 04Z 0.19 1625  97  93  12 0.16
Wed 07/29 05Z 0.20 1627  95  94  12 0.09
Wed 07/29 06Z 0.25 1627  94  95  12 0.05
Wed 07/29 07Z 0.33 1526  94  96  12 0.03
Wed 07/29 08Z 0.41 1527  94  96  12 0.03
Wed 07/29 09Z 0.49 1429  93  94  12 0.05
Wed 07/29 10Z 0.64 1331  92  95  11 0.08
Wed 07/29 11Z 0.73 1331  92  95  11 0.13
Wed 07/29 12Z 0.71 1335  91  96  11 0.13
Wed 07/29 13Z 0.72 1236  90  95  11 0.08
Wed 07/29 14Z 0.78 1237  91  94  11 0.05
Wed 07/29 15Z 0.82 1237  92  93  11 0.05
Wed 07/29 16Z 0.86 1237  91  92  11 0.04
Wed 07/29 17Z 0.85 1237  92  93  11 0.03
Wed 07/29 18Z 0.82 1235  93  92  11 0.03
Wed 07/29 19Z 0.78 1233  92  93  11 0.03
Wed 07/29 20Z 0.77 1131  93  92  12 0.02
Wed 07/29 21Z 0.74 1129  93  94  12 0.02
Wed 07/29 22Z 0.69 1128  93  95  12 0.01
Wed 07/29 23Z 0.69 1128  92  95  12 0.01

Run total areal avg QPF for the greens is: 2.64 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